GM Service Manual Online
For 1990-2009 cars only

Circuit Description

This diagnostic applies to internal microprocessor integrity conditions within the engine control module (ECM). This diagnostic also addresses if the ECM is not programmed.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC P0601 Control Module Read Only Memory (ROM)
    • DTC P0602 Control Module Not Programmed
    • DTC P0604 Control Module Random Access Memory (RAM)
    • DTC P0606 Control Module Internal Performance

Conditions for Running the DTC

DTC P0601

The checksum calculation at power down in the last drive cycle completely finished. DTC P0601 runs once an ignition cycle.

DTC P0602

The ignition is ON, with the engine OFF. DTC P0602 runs continuously.

DTC P0604

The read/write test at power down in the last drive cycle completely finished. DTC P0604 runs once an ignition cycle.

DTC P0606

DTC P0606 runs continuously with ignition ON or engine operating.

Conditions for Setting DTC

DTC P0601

The ECM detects the incorrect read only memory (ROM) checksum for more than 30 seconds.

DTC P0602

The ECM detects that programming is incomplete for more than 1 second.

DTC P0604

The ECM detects random access memory (RAM) errors for more than 5 seconds.

DTC P0606

The ECM detects an internal condition for more than 5 seconds.

Action Taken When the DTC Sets

    • The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC

    • The control module turns OFF the malfunction indicator lamp (MIL) after 4 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

    • For an intermittent condition, refer to Intermittent Conditions .
    • For complete details on programming the ECM, refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. A DTC P0602 indicates the ECM is not programmed.

  2. Attempt to program the ECM. If the ECM fails to program a second time, replace the ECM.

DTC P0601, P0602, P0604, P0605, P0606

Step

Action

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Ignition ON.
  2. Observe the DTC information, with a scan tool.

Does DTC P0601 or P0604 fail this ignition?

Go to Step 8

Go to Step 3

3

Is DTC P0602 set?

Go to Step 4

Go to Step 6

4

Program the engine control module (ECM). Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Does DTC P0602 reset?

Go to Step 5

Go to Step 9

5

  1. Ensure that all tool connections are secure.
  2. Ensure the programming equipment is operating correctly.
  3. Ensure the correct software and the correct calibration is used.
  4. Attempt to program the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Does DTC P0602 reset?

Go to Step 8

Go to Step 9

6

Is DTC P0606 set?

Go to Step 7

--

7

  1. Observe the Freeze Frame/Failure Records with a scan tool.
  2. Clear the DTCs with a scan tool.
  3. Turn OFF the ignition for 30 seconds.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did DTC P0606 fail this ignition?

Go to Step 8

Go to Diagnostic Aids

8

Replace the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 9

--

9

  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 2

Go to Step 10

10

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK