Circuit/System Verification

NOTE:

Repair all fuel system related DTCs, except P2635, before performing this diagnostic.
Inspect the fuel system for damage or external leaks before proceeding.
Verify that adequate fuel is in the fuel tank before proceeding.
The Fuel Pump Enable may need to be commanded On a few times in order to obtain the highest possible fuel pressure.
Before proceeding with this test review the User Manual CH 48027-5 for Safety Information and Instructions.

Ignition OFF, all accessories OFF, install a CH 48027 Gauge.
Ignition ON, engine OFF, command the Fuel Pump Enable On several times with a scan tool.
NOTE: DO NOT perform the Fuel System Diagnosis if the engine coolant temperature is above 60°C (150°F). High fuel pressure readings may result due to hot soak fuel boiling. With the engine OFF, the fuel pressure may increase beyond the pressure relief regulator valve's setting point of 690 kPa (100 psi) ± 5 percent.
Verify the fuel pressure is between 345-650 kPa (50-94 psi) with the fuel pump running.
- If less than 345 kPa (50 psi)
  Refer to Fuel Pressure Low .
- If greater than 650 kPa (94 psi)
  Replace the G12 Fuel Pump.
- If between 345-650 kPa (50-94 psi)
Verify that the fuel pressure decreases to less than 600 kPa (87 psi) after the fuel pump is turned off.
- If greater than 600 kPa (87 psi)
  Replace the G12 Fuel Pump.
- If less than 600 kPa (87 psi)
Verify that the fuel pressure does not decrease more than 34 kPa (5 psi) in 1 minute.
- If greater than 34 kPa (5 psi)
  Refer to Fuel Pressure Leaks Down .
- If less than 34 kPa (5 psi)
Relieve the fuel pressure to 69 kPa (10 psi).
Verify that the fuel pressure does not decrease more than 14 kPa (2 psi) in 5 min.
- If greater than 14 kPa (2 psi)
  Replace the G12 Fuel Pump.
- If less than 14 kPa (2 psi)
Engine idling.
Verify the Chassis Control Module Fuel Pressure Sensor parameter is between 300-400 kPa (43-58 psi).
- If less than 300 kPa (43 psi)
  Refer to Fuel Pressure Low .
- If greater than 400 kPa (58 psi)
  Replace the G12 Fuel Pump.
- If between 300-400 kPa (43-58 psi)
Verify the scan tool Short Term Fuel Pump Trim and the Long Term Fuel Pump Trim when multiplied together are less than 1.5.
- If greater than 1.5
  Refer to Fuel Pressure Low .
- If less than 1.5
Verify the scan tool Fuel Pressure Sensor and the Desired Fuel Pressure are within 45 kPa (6.5 psi) at 300 kPa (43.5 psi) request or 60 kPa (8.7 psi) at 400 kPa (58 psi) request of each other while operating the vehicle through varying loads.
- If greater than 45 kPa (6.5 psi)/60 kPa (8.7 psi)
  Refer to Fuel Pressure Drops Off .
- If less than 45 kPa (6.5 psi)/60 kPa (8.7 psi)
If the fuel system components test normal, refer to Symptoms - Engine Controls and Fuel Injector Diagnosis .