Circuit/System Verification

WARNING: This page is about a different car, the 2019 GMC Savana 3500, 2019 GMC Savana 2500, 2019 Chevrolet Express 3500, and 2019 Chevrolet Express 2500. However, it is still accessible from the selected car via links, so may be relevant.

NOTE:

This diagnostic assumes the following:

The battery is completely charged.
The engine cranking speed is acceptable.
There is adequate fuel in the fuel tank.

Crank the engine for up to 15 seconds.
Verify that DTC P0117, P0118, P0122, P0123, P0201 - P0208, P0222, P0223, P0300 - P0308, P0335, P0336, P0351 - P0358, P0562, P0563, P0601 - P0604, P0606, P0607, P062F, P0633, P0685, P0690, P1631, P1682, or P2610 is not set.
- If any of the DTCs are set
  Refer to Diagnostic Trouble Code (DTC) List - Vehicle .
- Go to next step: If none of the DTCs are set
Ignition ON
Verify the security indicator on the instrument cluster illuminates momentarily.
- If the security indicator stays ON or is flashing
  Review the Diagnostic Trouble Code (DTC) List - Vehicle , for Immobilizer system DTCs. For additional information, refer to Immobilizer Description and Operation .
- Go to next step: If the security indicator does not stay ON and is not flashing
Verify the scan tool Engine Speed parameter displays greater than 0 RPM while cranking the engine.
- If 0 RPM
  Refer to DTC P0335 or P0336 .
- Go to next step: If greater than 0 RPM
Ignition OFF, disconnect a spark plug wire from one of the spark plugs.
Connect the EL 26792 HEI Spark Tester between the spark plug boot and ground.

NOTE:

Perform the spark test on at least one cylinder from each engine bank.
An erratic or weak spark is considered a no spark condition.

Verify the spark tester sparks while cranking the engine.
- If the spark tester does not spark
  Refer to Electronic Ignition System Diagnosis .
- Go to next step: If the spark tester sparks
Verify all four CNG fuel tank manual shut-off valves are OPEN.
Verify the 1/4 turn manual shut-off valve is OPEN.
Ignition OFF, install the CH-48027 Digital Pressure Gauge. Refer to Fuel Pressure Gauge Installation and Removal .

NOTE:

Before proceeding with this test review the User Manual CH 48027-5 for Safety Information and Instructions.
If the engine is too hot, high fuel pressure readings may result due to hot soak fuel boiling. Allow the engine coolant temperature to cool to less than 60° C (150° F) before attempting to verify fuel pressure.
The Fuel Pump Relay may need to be commanded On several times in order to obtain the highest possible fuel pressure.
Additional DTCs may set when using the fuel pump relay output control.

Ignition ON.
Command the Fuel Pump Relay On several times with a scan tool.
Verify the fuel pressure is between 620 - 758 kPa (90 - 110 psi).
- If not within the specified range
  Refer to Fuel System Diagnosis (Without FPCM) , or Fuel System Diagnosis (FPCM) .
- Go to next step: If within the specified range
Verify the fuel pressure does not decrease greater than 34 kPa (5 psi) in 1 min.
- If not within the specified range
  Refer to Fuel System Diagnosis (Without FPCM) , or Fuel System Diagnosis (FPCM) .
- Go to next step: If within the specified range
Verify the conditions listed below do not exist:
- Collapsed air intake duct to the throttle body
- Restricted air filter element
- Gas or oil fouled spark plugs - Refer to Spark Plug Inspection
- A skewed manifold absolute pressure (MAP) sensor - Refer to DTC P0106 .
- A skewed engine coolant temperature (ECT) sensor - Refer to DTC P0116-P0119 .
- Restricted exhaust system - Refer to Restricted Exhaust .
- An engine mechanical condition, for example, worn timing chain or low compression - Refer to Symptoms - Engine Mechanical , and Camshaft Timing Chain and Sprocket Cleaning and Inspection .
- If a condition exists
  Repair as necessary.
- Go to next step: If no condition exists
All OK.