GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2006 🢒 Terraza - 4WD 🢒 Brakes 🢒 Park Brake 🢒 DTC P0601, P0602, P0603, P0604, P0605, P0606, P0607, P1600, P1621, P1627, P1680, P1681, P1683, or P2610

DTC Descriptors

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

DTC P2610: Control Module Ignition Off Timer Performance

Circuit/System Description

This diagnostic applies to internal microprocessor integrity conditions within the powertrain control module (PCM) and the throttle actuator control (TAC) system. This diagnostic also addresses if the PCM is not programmed.

The PCM monitors its ability to read and write to the memory. It also monitors a timing function. The PCM and the TAC processors are used to monitor the TAC system data. Both processors monitor the other processors data to verify that the indicated accelerator pedal position (APP) calculation is correct. The PCM performs an intrusive test in order to confirm that the APP signals are not shorted together. The PCM accomplishes this by pulling the APP sensor 2 low momentarily and looking for sensor 1 to also be pulled low.

Conditions for Running the DTC

P0601

The following conditions must be met:

    • The ignition switch is in Run or Crank.
    • The system voltage is more than 5 volts.

P0602

The following conditions must be met:

    • The ignition switch is in Run or Crank.
    • The controller is identified as a service replacement PCM.

P0604

The ignition switch is in Run or Crank.

P0606

The following conditions must be met:

    • The ignition switch is in Run or Crank.
    • During test function after Key Off before the control module powers down

P2610

The following condition must be met:

    • The ignition switch is in the OFF position for at least 1.6 seconds.
    • A low battery voltage or a battery disconnect condition has not taken place. Ignition OFF timer from the previous ignition cycle is stored.

Conditions for Setting the DTC

P0601

The PCM checksum value is incorrect for at least one sample. Each sample is 50 milliseconds. The PCM detects that the check sum value is incorrect for 0.05 second. This diagnostic runs continuously.

P0602

The PCM has not been programmed with Key On and Engine Off for one sample. Each sample is 100 milliseconds. The PCM has not been programmed at Key On and Engine Off for 0.1 second. This diagnostic runs continuously.

P0604

The PCM is unable to correctly write and read to and from random access memory (RAM) during the following conditions:

    • Key up initialization for one count. Each count is a read and write sample. Each sample is 100 milliseconds. This portion runs once per ignition cycle.
    • Counter increments by 10 for each sample that does not correctly read and write to the RAM, and decrements by 1 for each correct sample. No more than 20 counts which do not read and or write correctly. Each read and write sample is 100 milliseconds. This portion runs continuously.
    • Counter increments by 10 for each sample that does not correctly read and write to the desired throttle position RAM and decrements by 1 for each correct sample. No more than 20 counts which do not read and/or write correctly. Each read and write sample is 12.5 milliseconds. This portion runs continuously.

P0606

The PCM detects that the TAC system has a process sequence error, clock error, or processor is not operating correctly. Each test runs in 18.5 milliseconds. DTC sets after 200 milliseconds that a fault is detected.

P2610

This diagnostic has 2 tests that may set this DTC:

Phase 1

    • The PCM detects the ignition off timer is less than 1 second at any time.
        OR
    • The PCM detects the ignition off timer is 15 seconds or more if the actual elapsed time is less than 15 seconds.
    • This diagnostic runs continuous.

Phase 2

    • The last ignition off time event increments more than 1.375 seconds or less than 0.8 second for each second.
    • This diagnostic runs continuous.

Actions Taken When the DTC Sets

P0601, P0602, P0604, and P0606

    • 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.

P2610

    • The control module illuminates the MIL on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.
    • If the diagnostic reports a failure, the control module uses a cold start model based on the engine coolant temperature and intake air temperature at engine start-up. Using the cold start model ensures that the control module is able to determine how much time has elapsed between ignition cycles.

Conditions for Clearing the DTC
    • The control module turns OFF the MIL after 3 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.

Circuit/System Testing
  1. Observe the DTCs with the scan tool.
    2. ⇒If DTC P0602 is set, attempt to program the PCM before replacing the PCM. Refer to Service Programming System (SPS) .
    ⇒If DTC P0602 resets, replace the PCM.
  2. Test the voltage and ground circuits to the control module for the following conditions:
    3. • A short
    • An open
    • High resistance
    ⇒If all circuits test OK, replace the PCM.

Repair Instructions

Important: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for PCM replacement, programming and setup