Learning A TDC Offset (Cab & Chassis, Chevy Express, Cutaway, RV Cutaway, Savana, Savana Camper Special & Savana Special - 6.5L)

This procedure should only be used when a Diagnostic Trouble Code (DTC) has directed you to do so, or one of the following repairs has been performed:

• A DTC P1214 is set.
• The engine has been replaced.
• The front engine cover has been replaced.
• The Powertrain Control Module (PCM) and the injection pump have been replaced at the same time.
• The crankshaft position sensor has been replaced.

The PCM has the ability to perform a Top Dead Center (TDC) Offset Learn when one is not present or has been cleared. This procedure allows the PCM to be updated with the correct TDC offset for the vehicle.

The TDC Offset specification is only to be used after the Learn procedure has been performed. See TDC OFFSET SPECIFICATION  table.

1. One of the above repairs must have been performed. If not, do not continue.
2. Install the scan tool.
3. Start the engine.
4. Operate the vehicle until the Engine Coolant Temperature (ECT) is more than 170°F (77°C).
5. Clear all DTCs and turn the engine OFF.
6. Turn the ignition ON with the engine OFF.
7. Hold the accelerator pedal in the Wide Open Throttle (WOT) position for a minimum of 45 seconds (this step prepares the PCM to activate the offset learn (internal to PCM) and then release pedal.
8. Turn the ignition OFF for 30 seconds. In this step, the PCM powers down (to verify the PCM has powered down, a No Communication With Vehicle screen will display when trying to access a data list).
NOTE: A new TDC Offset will over write the previous one.
9. After the PCM has completed the power down, start the engine. Verify in the scan tool that the ECT is more than 170°F (77°C). If not, operate vehicle until desired ECT is achieved (vehicle can be driven or throttle can be depressed until correct coolant temperature is achieved). As soon as the ECT is more than 170°F (77°C) and the engine speed is below 1500 RPM, the PCM automatically learns a new offset (a momentary stumble in engine RPM will indicate that the TDC Offset has been activated).
10. Check the TDC Offset in the scan tool. The TDC Offset should be between -0.25 and -0.75. If the TDC Offset is within the specified value, the procedure is complete. If not, continue to the next step (adjusting the injection pump).
11. Turn the engine OFF.
12. Loosen injection pump flange nuts using the Injection Pump Wrench (J 41089).
NOTE: In order to achieve a negative (-) TDC Offset number, rotate the pump toward the drivers side of the vehicle. In order to achieve a positive (+) TDC Offset number, rotate the pump towards the passenger side of the vehicle.
13. Slightly (1 mm equals 2 degrees) rotate the injection pump in the desired direction (use the J 29872-A to rotate the injection pump) and then retighten the injection pump flange nuts (a scribe line across the pump flange and cover can be used as a reference (1 mm equals 2 degrees) which is the approximate width of a scribe line).
14. Repeat steps  3- 13 until the correct TDC Offset has been achieved. It is possible that the injection pump may require multiple adjustments to achieve the specified value. If you are unable to set the correct TDC Offset or the TDC Offset will not learn, check for the following:
    • The coolant temperature is more than 170°F (77°C).
    • Proper time intervals are observed for wide open throttle and PCM power down.
    • All PCM and injection timing stepper motor connections and for DTCs.
    • The Techline terminal/equipment for the latest software version.
    • For proper base installation of the injection pump (engine shut-down ESO solenoid should be approximately straight up and down).
    • If the TDC Offset is stuck on a high + (plus) value, check for a damaged camshaft driven gear key.
    • If the TDC Offset is stuck on a high - (negative) value, check for a damaged or improperly installed crankshaft position sensor.
    • If all checks have been performed, the injection pump may be malfunctioning, however, this is an extremely unlikely failure.