GM Service Manual Online
For 1990-2009 cars only

Object Number: 602567  Size: MF
Engine Controls Component Views
PCM Power and Grounds
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The powertrain control module (PCM) receives two ignition inputs from the ignition switch: IGN 0 and IGN 1. The PCM receives the Crank Request input with the ignition switch in the START position. The PCM uses a class 2 ignition mode message, and the voltage input from two separate systems to test the Crank Request circuit. If the PCM detects an improper input, DTC P0512 will set.

Conditions for Running the DTC

No Class 2 serial data circuit problem.

Conditions for Setting the DTC

The PCM detects an improper Crank Request input.

Action Taken When the DTC Sets

    • The PCM will not illuminate the malfunction indicator lamp (MIL).
    • The PCM will store conditions which were present when the DTC set as Fail Records information only.

Conditions for Clearing the MIL/DTC

    • The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
    • The DTC can be cleared by using the scan tool Clear DTC Information function.

Diagnostic Aids

If the condition is intermittent, refer to Intermittent Conditions in Symptoms.

Depending upon the circuit condition, symptoms of P0512 may be that the engine does not crank, or the engine cranks in the RUN position.

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Important: If the vehicle runs with the ignition turned OFF, repair the PCM Ignition 1 circuit for a short to B+.

Is DTC P1634 also set?

--

Go to Step 6

Go to Step 3

3

Does the engine crank with the ignition switch in the Run position?

--

Go to Step 4

Go to Diagnostic Aids

4

  1. Turn OFF the ignition.
  2. Disconnect the PCM connector.
  3. Connect test lamp between the Crank Request circuit and chassis ground.
  4. Observe the test lamp with the ignition switch in the RUN position.

Is the test lamp ON?

--

Go to Step 5

Go to Step 12

5

  1. Test the Crank Request circuit for a short to voltage.
  2. If the condition is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 11

6

  1. Turn OFF the ignition.
  2. Disconnect the PCM connector.
  3. Connect test lamp between the Crank Request circuit and chassis ground.
  4. Observe the test lamp while turning the ignition switch to the START position.

Is the test lamp ON?

--

Go to Step 7

Go to Step 8

7

  1. Inspect for poor terminal connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. If the condition is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

8

Inspect the Batt 2 fuse.

Is the fuse open?

--

Go to Step 9

Go to Step 10

9

  1. Test for a short to ground in the following circuits:
  2. • Ignition 1 circuit
    • Crank Request circuit
  3. If the condition is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

10

  1. Test for an open Crank Request circuit.
  2. If the condition is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 11

11

Replace the ignition switch. Refer to Steering Column Lock and Ignition Switch Cylinder Replacement - On Vehicle in Steering Wheel and Column - Tilt.

Is the action complete?

--

Go to Step 13

--

12

Important: The replacement PCM must be programmed.

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 13

--

13

  1. Review and record the scan tool Fail Record data.
  2. Clear the DTC(s).
  3. Turn ON the ignition, with the engine OFF.
  4. With the scan tool, observe the Specific DTC Information for DTC P0512 until the test runs.

Does the scan tool indicate that DTC P0512 passed?

--

System OK

Go to Step 2