Test Description

WARNING: This page does not describe the selected car, but rather 13 other vehicles, including the 2002 GMC Yukon XL, 2002 GMC Sierra, 2002 GMC Savana Special, 2002 GMC Savana Camper Special, and 2002 GMC Savana. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step number in the diagnostic procedures.

2

The 5-volt reference circuits for the sensors are connected together inside the PCM. Both DTCs P1635 and P1639 set at the same time indicates a 5-volt reference circuit is shorted to a voltage.

3

The 5-volt reference circuits for the sensors are connected together inside the PCM. When only DTC P1635 is set, this indicates a short to ground on one of the 5-volt reference circuits.

5

This step isolates the 5-volt reference circuit from the sensor signal circuit.

6

This step determines if the 5-volt reference circuits or the fuel level sensor signal circuit are only shorted when the fuel pump is enabled. You may have to enable the fuel pump a couple of times to see if the voltages increase. Inspect the fuel pump harness thoroughly for being shorted to the FTP sensor or the fuel level sensor.

8

The 5-volt reference circuits may be shorted to another PCM circuit. The shorted circuit may not be apparent when the PCM harness connector is disconnected. Testing continuity from each 5-volt reference circuit isolates the shorted circuit.