GMLAN serial links are an interconnect network (CAN), consisting of high-speed and low-speed serial data buses used for data exchange between controllers. Typical data rates must be high enough to provide the required response time for real-time operation.
There are two different types of GMLAN serial links: high speed 2-wire and low speed single wire. GMLAN serial links are also connected directly to the diagnostic socket (DLC). The messages are interpreted by an externally connected CANdi module, which serves as a converter for the diagnostic tool.
The controller that generated the DTC has attempted to communicate on the GMLAN lines more than 7 times.
- One of the low speed GMLAN serial links is shorted to ground or power.
- An internal fault in one of the controllers causing a short to voltage or ground in the low speed GMLAN circuits.
Step | Operation | Values | Yes | No |
1 |
Did you run a diagnostic system check?
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-
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Go to Step 2
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Check the vehicle with a diagnostic tool.
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2 |
Is the scan tool communicating with any controller connected to the low speed GMLAN link?
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-
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Go to Step 3
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Go to Step 5
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3 |
Are any DTCs received from U0140 and U0155?
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-
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Jump to the appropriate section for diagnosing DTCs
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Go to Step 4
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4 |
Test for an open or short to ground or voltage on the low speed GMLAN serial communications circuits at each connected controller.
Has the cause been found and fixed?
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-
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Go to Step 16
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Go to Step 5
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5 |
Has the cause been found and fixed?
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-
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Go to Step 13
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Go to Step 6
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6 |
Has the cause been found and fixed?
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-
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Check the vehicle with a diagnostic tool.
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Go to Step 7
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7 |
Does the scan tool communicate with the BCM?
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-
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Go to Step 11
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Go to Step 8
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8 |
Does the scan tool communicate with the BCM?
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-
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Go to Step 9
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Go to Step 10
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9 |
Test for a short to ground or short to voltage on the low speed GMLAN serial communications circuits between the last disconnected controllers.
Has the cause been found and fixed?
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B+
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Go to Step 9
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Go to Step 10
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10 |
Is the BCM the last device still connected to the low speed GMLAN serial link?
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-
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Go to Step 11
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Go to Step 8
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11 |
Has the cause been found and fixed?
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-
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Go to Step 14
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Go to Step 12
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12 |
Verify that there is no loose connection on the low speed GMLAN serial link circuit on the last disconnected controller.
Has the cause been found and fixed?
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-
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Go to Step 14
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Go to Step 13
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13 |
Replace the last disconnected controller.
Has the replacement been completed?
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-
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Go to Step 14
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-
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14 |
Are there any DTCs that begin with "U" and with the current status?
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-
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Go to Step 15
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15 |
Are there any DTCs that do not start with "U"?
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-
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Go to Step 16
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16 |
Have all DTCs been diagnosed?
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-
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Go to Step 17
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Go to Step 14
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17 |
Use a scan tool to clear the DTCs.
Is the action completed?
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-
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System OK
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-
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During normal vehicle operation, the controllers connected to the GMLAN serial link monitor the communication. Between the controllers there is an exchange of operational information and commands. The controllers have information about what messages should be exchanged over serial communication lines in each virtual network. These messages are also monitored and certain regular messages are used by the receiving controller to determine the availability of the sending controller. The validation timeout is 250 milliseconds. Each message contains the identification number of the transmitting controller. If a message indicating the availability of the transmitting controller is not received, the receiving controller issues a U01xx DTC, where "xx" is the 2-digit identification number of the transmitting controller.
For a controller that has a GMLAN serial link failure or power failure during the current ignition cycle, the DTC is "Communication failure" issued by other controllers that require data from this failed module. Controllers that have not lost communication will generate a fault code indicating the controller with broken communication.
- Controller supply voltages within normal operating range
- Serial communication is required for the vehicle power mode to work.
- DTC U0073 has no current status
- This DTC may be set due to a broken contact in the failed controller.
- This DTC may be issued due to a power failure in the controller.
Step | Operation | Values | Yes | No |
1 |
Did you run a diagnostic system check?
|
-
|
Go to Step 2
|
Check the vehicle with a diagnostic tool.
|
2 |
Test for an open or short to ground or voltage on the low speed GMLAN serial link circuit at the BCM.
Has the cause been found and fixed?
|
-
|
Go to Step 6
|
Go to Step 3
|
3 |
Check the BCM connector for loose connections.
Has the cause been found and fixed?
|
-
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Go to Step 6
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Go to Step 4
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4 |
Has the cause been found and fixed?
|
-
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Go to Step 6
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Go to Step 5
|
5 |
Has the replacement been completed?
|
-
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Go to Step 6
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-
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6 |
Does the scan tool display any DTCs that do not begin with "U"?
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-
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Jump to the appropriate section for diagnosing DTCs
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Go to Step 7
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7 |
Select the function of reading fault codes for the SDM controller.
Does the scan tool display any DTCs that do not begin with "U"?
|
-
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Jump to the appropriate section for diagnosing DTCs
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Go to Step 8
|
8 |
Is the action completed?
|
-
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System OK
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-
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DTC U0151 00: Lost communication with sensor and diagnostic controller (SDM)
Controllers connected to the high and low speed GMLAN serial links monitor serial communications during normal vehicle operation. Between the controllers there is an exchange of operational information and commands. The controllers have pre-recorded information about what messages should be exchanged over the serial links in each virtual network. These messages are monitored and in addition certain regular messages are used by the receiving controller to determine the availability of the sending controller. Each message contains the identification number of the transmitting controller.
body controller (BCM) activates the serial line enable and auxiliary wake-up circuits for the serial line by applying voltage when the ignition switch is in the ACC, ON, or START position. Serial link enable circuit wakes up brake controller (EBCM) for bus communication, and an auxiliary serial line wake-up circuit wakes up the motor controller (ECM) and gearbox controller (TCM).
- Serial communication is required for the vehicle power mode master to operate.
- Serial communication is required for the vehicle power mode to work.
A monitored regular message indicating the availability of the transmitting controller was not received.
The controllers have never signaled, so certain subsystems will not work.
- The current fault code is cleared after the fault disappears.
- The DTC is cleared from the log when the ignition cycle counter in the controller reaches the reset threshold of 50 without recurring the fault.
- Using the above list of DTC definitions, determine which of the controllers is out of communication.
- If there are several controllers with communication failure, select the one closest to the diagnostic socket (DLC).
- Use the link list to determine whether the GMLAN serial link on this controller is high speed or low speed.
- Some controllers lack internal protection for certain voltage outputs and may cause the battery positive voltage fuse or ignition voltage source to blow. If the input voltage fuse is blown but no short circuit is detected on this circuit, verify that the controllers do not have a voltage output circuit shorted to ground before replacing the controller.
- This diagnostic can be applied to any controller that needs to communicate over a high or low speed GMLAN serial link, provided the vehicle is equipped with the option that uses this controller.
- Use the above list of DTC definitions and diagnostic tips to determine which controller is out of communication to check.
- Ignition OFF, disconnect the harness connector at the controller that is not communicating.
Important: Only high speed GMLAN controllers have a serial line enable circuit OR an auxiliary serial line wakeup circuit. Refer to the controller diagrams to determine which controllers have these circuits. If the offending controller is missing one of these circuits, go to step 4.
- Ignition ON, verify the test lamp illuminates between the serial link enable circuit OR the serial link auxiliary wakeup circuit and ground.
- If the test lamp does not illuminate, repair the open or high resistance in the circuit. If there are no open circuits, replace the BCM.
- Ignition ON, test for a test lamp illuminated between all of the battery positive voltage circuits and ground.
- If the test lamp does not illuminate, repair the short to ground or open/high resistance in the circuit. If the circuit fuse is blown, also check the positive voltage outputs on the controller for a short to ground. If the circuits are OK, replace the failed controller.
- Test for a test lamp illuminated between all ignition voltage circuits and ground.
- If the test lamp does not illuminate, repair the short to ground or open/high resistance in the circuit. If the circuit fuse is blown, also check the positive voltage outputs on the controller for a short to ground. If the circuits are OK, replace the failed controller.
- Verify that the resistance between the controller ground circuits and ground is less than 1 ohm.
- If it is greater than 1 ohm, repair the open in the ground circuit.
- Use the link list to determine if the offending controller is using a low speed GMLAN serial link.
- If the controller only uses high speed GMLAN, replace the controller.
- Verify that the low speed GMLAN serial link circuit resistance between the offending controller and the controller issuing the DTC is less than 1 ohm.
- If resistance is greater than 1 Ω, test the low speed GMLAN serial link circuit for an open or high resistance.
- If all circuits are OK, replace the controller with the communication problem.
Perform a post-repair diagnostic check after completing the diagnostic procedure. Controller information for replacing, configuring and programming the BCM. See Section 9V, "body controller".
DTC U0168 00: Lost Communication with Vehicle Theft Deterrent System Controller (VTD)
Controllers connected to the high and low speed GMLAN serial links monitor serial communications during normal vehicle operation. Between the controllers there is an exchange of operational information and commands. The controllers have pre-recorded information about what messages should be exchanged over the serial links in each virtual network. These messages are monitored and in addition certain regular messages are used by the receiving controller to determine the availability of the sending controller. Each message contains the identification number of the transmitting controller.
body controller (BCM) activates the serial line enable and auxiliary wake-up circuits for the serial line by applying voltage when the ignition switch is in the ACC, ON, or START position. Serial link enable circuit wakes up brake controller (EBCM) for bus communication, and an auxiliary serial line wake-up circuit wakes up the motor controller (ECM) and gearbox controller (TCM).
- The voltage in the system is 9 - 16 V.
- Serial communication is required for the vehicle power mode master to operate.
A monitored regular message indicating the availability of the transmitting controller was not received.
The controllers have never signaled, so certain subsystems will not work.
- The current fault code is cleared after the fault disappears.
- The DTC is cleared from the log when the ignition cycle counter in the controller reaches the reset threshold of 50 without recurring the fault.
- Using the above list of DTC definitions, determine which of the controllers is out of communication.
- If there are several controllers with communication failure, select the one closest to the diagnostic socket (DLC).
- Use the link list to determine whether the GMLAN serial link on this controller is high speed or low speed.
- Some controllers lack internal protection for certain voltage outputs and may cause the battery positive voltage fuse or ignition voltage source to blow. If the input voltage fuse is blown but no short circuit is detected on this circuit, verify that the controllers do not have a voltage output circuit shorted to ground before replacing the controller.
- This diagnostic can be applied to any controller that needs to communicate over a high or low speed GMLAN serial link, provided the vehicle is equipped with the option that uses this controller.
- Use the above list of DTC definitions and diagnostic tips to determine which controller is out of communication to check.
- Ignition OFF, disconnect the harness connector at the controller that is not communicating.
Important: Only high speed GMLAN controllers have a serial line enable circuit OR an auxiliary serial line wakeup circuit. Refer to the controller diagrams to determine which controllers have these circuits. If the offending controller is missing one of these circuits, go to step 4.
- Ignition ON, verify the test lamp illuminates between the serial link enable circuit OR the serial link auxiliary wakeup circuit and ground.
- If the test lamp does not illuminate, repair the open or high resistance in the circuit. If there are no open circuits, replace the BCM.
- Ignition ON, test for a test lamp illuminated between all of the battery positive voltage circuits and ground.
- If the test lamp does not illuminate, repair the short to ground or open/high resistance in the circuit. If the circuit fuse is blown, also check the positive voltage outputs on the controller for a short to ground. If the circuits are OK, replace the failed controller.
- Test for a test lamp illuminated between all ignition voltage circuits and ground.
- If the test lamp does not illuminate, repair the short to ground or open/high resistance in the circuit. If the circuit fuse is blown, also check the positive voltage outputs on the controller for a short to ground. If the circuits are OK, replace the failed controller.
- Verify that the resistance between the controller ground circuits and ground is less than 1 ohm.
- If it is greater than 1 ohm, repair the open in the ground circuit.
- Use the link list to determine if the offending controller is using a low speed GMLAN serial link.
- If the controller only uses high speed GMLAN, replace the controller.
- Verify that the low speed GMLAN serial link circuit resistance between the offending controller and the controller issuing the DTC is less than 1 ohm.
- If resistance is greater than 1 Ω, test the low speed GMLAN serial link circuit for an open or high resistance.
- If all circuits are OK, replace the controller with the communication problem.
Perform a post-repair diagnostic check after completing the diagnostic procedure.
DTC U0214 00: Lost communication with remote activation controller (RFA)
Controllers connected to the high and low speed GMLAN serial links monitor serial communications during normal vehicle operation. Between the controllers there is an exchange of operational information and commands. The controllers have pre-recorded information about what messages should be exchanged over the serial links in each virtual network. These messages are monitored and in addition certain regular messages are used by the receiving controller to determine the availability of the sending controller. Each message contains the identification number of the transmitting controller.
body controller (BCM) activates the serial line enable and auxiliary wake-up circuits for the serial line by applying voltage when the ignition switch is in the ACC, ON, or START position. Serial link enable circuit wakes up brake controller (EBCM) for bus communication, and an auxiliary serial line wake-up circuit wakes up the motor controller (ECM) and gearbox controller (TCM).
- The voltage in the system is 9 - 16 V.
- Serial communication is required for the vehicle power mode master to operate.
A monitored regular message indicating the availability of the transmitting controller was not received.
The controllers have never signaled, so certain subsystems will not work.
- The current fault code is cleared after the fault disappears.
- The DTC is cleared from the log when the ignition cycle counter in the controller reaches the reset threshold of 50 without recurring the fault.
- Using the above list of DTC definitions, determine which of the controllers is out of communication.
- If there are several controllers with communication failure, select the one closest to the diagnostic socket (DLC).
- Use the link list to determine whether the GMLAN serial link on this controller is high speed or low speed.
- Some controllers lack internal protection for certain voltage outputs and may cause the battery positive voltage fuse or ignition voltage source to blow. If the input voltage fuse is blown but no short circuit is detected on this circuit, verify that the controllers do not have a voltage output circuit shorted to ground before replacing the controller.
- This diagnostic can be applied to any controller that needs to communicate over a high or low speed GMLAN serial link, provided the vehicle is equipped with the option that uses this controller.
- Use the above list of DTC definitions and diagnostic tips to determine which controller is out of communication to check.
- Ignition OFF, disconnect the harness connector at the controller that is not communicating.
Important: Only high speed GMLAN controllers have a serial line enable circuit OR an auxiliary serial line wakeup circuit. Refer to the controller diagrams to determine which controllers have these circuits. If the offending controller is missing one of these circuits, go to step 4.
- Ignition ON, verify the test lamp illuminates between the serial link enable circuit OR the serial link auxiliary wakeup circuit and ground.
- If the test lamp does not illuminate, repair the open or high resistance in the circuit. If there are no open circuits, replace the BCM.
- Ignition ON, test for a test lamp illuminated between all of the battery positive voltage circuits and ground.
- If the test lamp does not illuminate, repair the short to ground or open/high resistance in the circuit. If the circuit fuse is blown, also check the positive voltage outputs on the controller for a short to ground. If the circuits are OK, replace the failed controller.
- Test for a test lamp illuminated between all ignition voltage circuits and ground.
- If the test lamp does not illuminate, repair the short to ground or open/high resistance in the circuit. If the circuit fuse is blown, also check the positive voltage outputs on the controller for a short to ground. If the circuits are OK, replace the failed controller.
- Verify that the resistance between the controller ground circuits and ground is less than 1 ohm.
- If it is greater than 1 ohm, repair the open in the ground circuit.
- Use the link list to determine if the offending controller is using a low speed GMLAN serial link.
- If the controller only uses high speed GMLAN, replace the controller.
- Verify that the low speed GMLAN serial link circuit resistance between the offending controller and the controller issuing the DTC is less than 1 ohm.
- If resistance is greater than 1 Ω, test the low speed GMLAN serial link circuit for an open or high resistance.
- If all circuits are OK, replace the controller with the communication problem.
Perform a post-repair diagnostic check after completing the diagnostic procedure.
DTC B1325 03: Low Battery Voltage
DTC B1325 07: High Battery Voltage
The controllers on this vehicle monitor battery voltage through the battery positive voltage circuits. There are many controllers on the vehicle that can generate this DTC.
The voltage supplied to the controllers is in the range of 7-18 V.
DTC B1325 03
- The controller detects that the system voltage is below a calibrated value, typically 7.8V.
- The above condition persists for at least 1 second.
DTC B1325 07
- The controller detects that the system voltage is above a calibrated value, typically 18V.
- The above condition persists for at least 1 second.
- The controller immediately disables all outputs when an out-of-voltage voltage is detected, except for GMLAN and relays "Work/Start", which turn off after a 3-minute delay.
- The issuance of other fault codes is blocked.
- The current fault code is cleared after the fault disappears.
- The fault code is cleared from the log when the ignition cycle counter in the controller reaches the reset threshold without recurring the fault.
Step | Operation | Values | Yes | No |
1 |
Has the vehicle system diagnostic check been completed?
|
-
|
Go to Step 2
|
Check the vehicle with a diagnostic tool.
|
2 |
Is the displayed value of the parameter "battery voltage" within the specified range?
|
9 - 18 V
|
Go to Step 3
|
Go to Step 4
|
3 |
DTC issued as current?
|
-
|
Go to Step 7
|
|
4 |
Is the measured value within the specified range?
|
-
|
Go to Step 6
|
Go to Step 5
|
5 |
Check the battery positive voltage circuit for the following:
Has the cause been found and fixed?
|
-
|
Go to Step 9
|
|
6 |
Test all controller ground circuits for an open or high resistance.
Has the cause been found and fixed?
|
-
|
Go to Step 9
|
Go to Step 7
|
7 |
Inspect the harness connector on the controller under test for loose connections. See section 9A "Intermittent Fault Check in Body Wiring System".
Has the cause been found and fixed?
|
-
|
Go to Step 9
|
Go to Step 8
|
8 |
Replace defective controller. See the controller manual for replacement, setup, and programming procedures.
Has the replacement been completed?
|
-
|
Go to Step 9
|
-
|
9 |
Operate the system to check if the problem has been fixed.
Has the cause been found and fixed?
|
-
|
System OK
|
Go to Step 2
|
DTC B0158 0E - OAT Sensor Circuit Below Threshold
DTC B0158 0D - OAT Sensor Circuit Above Threshold
The controllers on this vehicle monitor battery voltage through the battery positive voltage circuits. There are many controllers on the vehicle that can generate this DTC.
Ignition switch in ACC or RUN position
DTC B0158 0E
- Once the resistance is out of range, the code will remain current until the resistance drops below 0.28 ohms for 1 second.
DTC B0158 0D
- Once the resistance is out of range, the code will remain current until the resistance rises above 36.1 kΩ for 1 second.
- The fault code will be logged if the HVAC controller (HVAC) will no longer detect the conditions for issuing this DTC.
- The current fault code is cleared after the fault disappears.
The numbers below represent the steps in the diagnostic table.
- This step tests the correct operation of the circuit in the upper voltage range.
- This step tests the circuit for proper operation in the lower voltage range. If the jumper fuse blows during this test, the signal circuit is shorted to supply voltage.
Step | Operation | Values | Yes | No |
1 |
Has the vehicle system diagnostic check been completed?
|
-
|
Go to Step 2
|
Check the vehicle with a diagnostic tool.
|
2 |
Does the scan tool indicate that the relevant parameter is within the specified range?
|
0.3 ohm ~ 3.6 k ohm
|
Go to Step 3
|
|
3 |
Does the scan tool indicate that the appropriate parameter is greater than the specified value?
|
0.3 ohm
|
Go to Step 4
|
Go to Step 5
|
4 |
Does the scan tool indicate that the appropriate parameter is less than the specified value?
|
3.6 kOhm
|
Go to Step 9
|
Go to Step 6
|
5 |
Test the signal circuit of the appropriate outside air temperature sensor for a short to ground.
Has the cause been found and fixed?
|
-
|
Go to Step 13
|
Go to Step 10
|
6 |
Test the signal circuit of the appropriate outside air temperature sensor for a short to voltage, high resistance, or an open.
Has the cause been found and fixed?
|
-
|
Go to Step 13
|
Go to Step 7
|
7 |
Test the low reference circuit of the appropriate outside air temperature sensor for a high resistance or an open.
Has the cause been found and fixed?
|
-
|
Go to Step 13
|
Go to Step 8
|
8 |
Test the following signal circuits for a short to voltage:
Has the cause been found and fixed?
|
-
|
Go to Step 13
|
Go to Step 10
|
9 |
Inspect the harness connector of the appropriate outside air temperature sensor for loose connections. Go to Section 9A "Intermittent Fault Check in Body Wiring System".
Has the cause been found and fixed?
|
-
|
Go to Step 13
|
Go to Step 11
|
10 |
Check harness connector at HVAC controller (HVAC) for contact violations. Go to Section 9A "Intermittent Fault Check in Body Wiring System".
Has the cause been found and fixed?
|
-
|
Go to Step 13
|
Go to Step 12
|
11 |
Replace the corresponding outdoor temperature sensor.
Has the replacement been completed?
|
-
|
Go to Step 13
|
-
|
12 |
Replace HVAC controller. See Section 7D, Automatic Temperature Control, Heating, Ventilation and Air Conditioning System.
Has the replacement been completed?
|
-
|
Go to Step 13
|
-
|
13 |
Is the DTC cleared?
|
-
|
Go to Step 2
|
System OK
|