Removing the ECM/PCM
1. ECM electronic control unit (PCM control unit) located in the car under the dashboard (Right side).
2. Disconnect the wires from the battery.
3. Remove the screws securing the decorative panel under the right side of the dashboard.
4. Remove the decorative panel, thus opening access to the patch panel (see illustration).
3.4. Remove the lower trim panel under the glove box to expose the junction panel and ECM/PCM
5. Disconnect both electrical connectors from the ECM/PCM (see illustration).
3.5. Press hard on the plates (shown by arrows) for disconnecting electrical connectors from the ECM/PCM
Attention! When disconnecting and connecting electrical connectors, the ignition must be turned off to prevent damage to the ECM/PCM.
6. Loosen the fastening nut (see illustration) on the left side of the ECM/PCM.
3.6. Loosen the fastening nut (shown by arrow) computer to holder
7. Gently slide the ECM/PCM down to expose the fuse panel.
Attention! To prevent damage to the computer from static electricity, wear gloves and use a special anti-static pad to store the ECM/PCM after removal.
General description
PROM (engine 3.1 l)
8. To allow the same ECM model to be used on different vehicles (see illustration), using a device called a PROM (programmable read only memory). To gain access to the PROM, the cover must be removed. The PROM is located inside the ECM (see illustration) and contains information about the mass of the vehicle, engine, transmission, final drive ratio, etc. An ECM with a specific serial number can be used in many vehicles manufactured "General Motors" (GM), but each PROM can only be used on the vehicle for which it was designed. Therefore, it is necessary to check the latest editions of the spare parts catalogs and service bulletins for information about the serial numbers of PROMs when they are replaced. The ECM is usually purchased without a PROM. Carefully remove the PROM chip from the old ECM and install it on the new ECM.
3.8a. If you are replacing the ECM, compare the service numbers on the labels of the new and old ECM | 3.8b. PROM position (shown by arrow) in the ECM for the 3.1L engine (the PCM block for the 3.8 liter engine is designed similarly, only the MEM-CAL device is installed instead of the PROM and CALPAK |
CALPAK (engine 3.1 l)
9. A device called CALPAK is used to provide fuel in the event of failure of other ECM components. If the CALPAK fails, a new ECM must be installed.
MEM-CAL (engine 3.8 l)
10. The MEM-CAL device includes the functions of the PROM, CALPAK and ESC block used on other cars of production "General Motors". Like the PROM, it contains the calibration information of the vehicle, as well as an emergency fuel control circuit in the event of failure of the remaining PCM components.
Replacing elements
PROM (engine 3.1 l)
11. Turn the ECM upside down and place it on a clean work surface.
12. Remove the PROM/CALPAK protective cover.
13. Using a PROM removal tool, pry off the PROM holder from the narrow ends (see illustration). Slightly rock the holder from side to side and pull it up. PROM together with the holder should easily come out of the socket.
3.13. Using a PROM remover, pry off the PROM holder from the side of the narrow ends and slightly shake the device with the holder until the PROM comes out of the socket: 1 - PROM holder, 2 - PROM extractor
Attention! The PROM holder must only be removed using a special tool. Removal without this device or with the help of other devices may damage the PROM chip or its socket.
14. Before putting the PROM holder aside, remember its position in the installed state (see illustration).
3.14. Remember the mutual orientation of the notch on the PROM and the smaller notch on the holder: 1 - PROM holder, 2 - PROM, 3 - recess in the PROM is consistent with the small recess in the holder and the label
15. If you are replacing the ECM, remove the new ECM from its holder, check its service number and make sure it matches the number on the old ECM (see illustration 3.8a).
16. If you are replacing the PROM, remove the new PROM from its holder, check its service number and make sure it matches the number on the old PROM.
17. Position the block "PROM/PROM holder" perpendicular to the socket so that the recess on the holder is aligned with the recess in the socket on the side of the 1st contact. Press down on the PROM holder until it is firmly seated in place (see illustration).
3.17. Press only on the ends of the PROM holder - pressing on the inside may cause the contact pins to bend or break or cause the PROM to fail
18. When installing a new PROM, make sure that the notch on it is aligned with the small notch on the holder.
Attention. If the PROM is installed the other way around, then when the ignition is turned on, it will fail.
19. Using the tool, install the new PROM holder into the PROM socket in the ECM. The recess on the holder must be aligned with the recess in the socket. Press down on the PROM holder until it is firmly seated.
Attention! Do not press on the PROM chip - only on the holder.
20. Install the protective cover on the ECM and tighten the two screws.
21. Install the ECM on the bracket, connect the electrical connectors to it and install it under the dashboard.
22. Start the engine.
23. Set the diagnostic mode by connecting the ALDL diagnostic terminal to "weight" (see section 2). If no fault codes are displayed, the PROM is installed correctly.
24. If fault code 51 is displayed or the light comes on and stays on "SERVICE ENGINE SOON", then this may be due to incomplete fit of the PROM, installation of the PROM in the reverse position, bending of the contact pins, malfunction of the PROM.
25. If the problem is due to an incomplete seating of the PROM, it can be corrected by pressing firmly on both ends of the holder.
26. If the pins of the microcircuit are bent, remove the PROM, straighten the contacts and reinstall the PROM. If you break the contact during straightening, the PROM must be replaced with a new one.
27. If a careful check shows that the PROM is firmly seated, installed correctly and the contacts are not bent, and the lamp "SERVICE ENGINE SOON" stays lit, the PROM is most likely defective and should be replaced.
MEM-CAL (engine 3.8 l)
Note. In terms of removing the PCM from the vehicle, the procedures for replacing the MEM-CAL are similar to those for the PROM. However, the operations for removing and installing the MEM-CAL, as well as the functional check of the correctness of its installation, are somewhat different from the operations for PROM and CALPAK.
28. Remove the MEM-CAL protective cover.
29. Use two fingers to spread both clamps away from the MEM-CAL (see illustration). Grab both ends of the MEM-CAL at the same time and remove it from its socket. Do not remove the cover of the MEM-CAL unit.
3.29. Spread both clamps aside (shown by arrows) from the MEM-CAL unit and at the same time grasp both ends of the unit and remove it from the slot
Attention! Using other removal and installation methods may damage the MEM-CAL unit or its socket.
30. Make sure the numbers on the old and new PCM match (or numbers on old and new MEM-CAL, depending on what you are replacing), as described for removing and installing the PROM (see illustration 3.8a).
31. Push the ends of the MEM-CAL into the slot.
32. The notches on the MEM-CAL must align with notches 8 on the MEM-CAL connector. Press the ends of the MEM-CAL until both clips snap into place on the edges of the MEM-CAL. Do not click on the middle of the block - only on its edges (see illustration).
3.32. To install the MEM-CAL block, press only on the ends (shown by arrows). Make sure the notches on the MEM-CAL match the notches on the socket
33. The remaining installation operations are the same as those for the PROM.
34. After the new MEM-CAL unit is installed in the old PCM (or old MEM-CAL installed in new PCM), verify that the installation is correct by doing the following:
- A) Turn on the ignition.
- b) Set diagnostic mode to ALDL (see section 2).
- V) Wait until code 12 is displayed 4 times to make sure there are no other codes. This indicates that MEM-CAL is installed correctly and PCM is working properly.
35. If codes 41, 42, 43, 51 are displayed or the lamp lights up and stays on "SERVICE ENGINE SOON", this may be due to an incomplete fit or malfunction of the MEM-CAL If the MEM-CAL is loose, press firmly on its edges. If it is necessary to remove the MEM-CAL unit, follow the instructions above.