GM Service Manual Online
For 1990-2009 cars only

Object Number: 185025  Size: LF
Engine Controls Components
Ignition System
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The PCM has the ability to determine the amount of offset needed to bring the engine to top dead center. This is used by the PCM to determine proper injection time.

Conditions for Running the DTC

The ignition switch in the ON position.

Conditions for Setting the DTC

    • The TDC offset is greater than 2.46 degrees
        or
    • The TDC Offset is less than -2.46 degrees.

Action Taken When the DTC Sets

    • The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails.
    • The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the Failure Records will store this information. If the diagnostic reports a failure on the second consecutive drive trip, the Freeze Frame records the operating conditions at the time of failure and updates the Failure Records.

Conditions for Clearing the MIL/DTC

    • The PCM will turn the MIL off after three consecutive trips without a fault condition.
    • A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures
    • The use of a scan tool.

Diagnostic Aids

The PCM will only run the diagnostic test when a time set procedure has been activated. It is highly unlikely that the vehicle will be brought in with this DTC set. Refer to Fuel Injection Pump Top Dead Center Offset Adjustment .

Step

Action

Value(s)

Yes

No

1

Important: Before clearing any DTCs, use the scan tool Capture Info to save freeze frame and failure records for reference, as the Scan tool loses data when using the Clear Info function.

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Are there any other DTCs set?

--

Go to the Applicable DTC Table

Go to Step 3

3

Clear all codes and reset injection timing until TDC Offset is between specified values. Refer to Fuel Injection Pump Top Dead Center Offset Adjustment .

Is timing within specified value?

-0.25 to -0.75

Go to Step 6

Go to Step 4

4

Check the crankshaft position sensor for the following.

    • Proper installation.
    • Loose or broken sensor mounting tab.

Was a repair performed?

--

Go to Step 6

Go to Step 5

5

Replace the Injection Pump. Refer to Fuel Injection Pump Replacement .

Important: The new injection pump must be timed. Refer to Fuel Injection Pump Timing Adjustment .

Is the action complete?

--

Go to Step 6

--

6

  1. Using the Scan tool, clear the DTCs.
  2. Start engine and idle at normal operating temperature.
  3. Select DTC, Specific, then enter the DTC number which was set.
  4. Operate the vehicle, with the Conditions for Setting this DTC, until the Scan Tool indicates the diagnostic Ran.

Does the Scan Tool indicate the diagnostic Passed?

--

Go to Step 7

Go to Step 2

7

Does the Scan tool display any additional undiagnosed DTCs?

--

Go to the Applicable DTC Table

System OK