2007-2008 Duramax Diesel Five Volt Reference Information - keywords 6.6 6.6L cal calibration circuit DTC ECM ground LMM MIL open P0642 P0643 P0651 P0652 P0653 ref reference short volt voltage wire

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

This is an informational PI for technicians that may be in process of diagnosing a five volt reference sensor or circuit.

A technician may encounter a diagnostic code which involves testing of the wiring circuits to a 5 volt reference sensor. A five volt reference circuit tested when voltage is present will return a false resistance reading.

Before testing the related circuits ensure that the ECM is fully powered down.

1. If the Tech 2 is connected to the DLC (Data Link Connector) it may keep the ECM awake for longer than 90 seconds after turning the ignition OFF. To ensure a good measurement, disconnect the scan tool from the DLC, turn the key off, and wait at least 90 seconds before the circuit resistance is checked.
2. The five volt reference circuit may remain active with retained accessory power. If the key is turned off by reaching through the window (door not opened and closed) the five volt reference circuits may still be active.

Note: When diagnosing a P0651 or P0652 (5 VOLT REFERENCE (X) CIRCUIT LOW VOLTAGE), technicians may observe low or no voltage on all supply circuits driven by a particular 5 volt reference bank. This is indicative of a short to ground and not necessarily a problem with the ECM. The ECM will purposely disable supply voltage to all sensors connected to that 5 volt reference bank. The ECM will restore supply voltage to the 5 volt reference circuit only after the short has been repaired.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.