Test Description
WARNING: This page is about a different car, the 2004 GMC Sierra and 2004 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The numbers below refer to the step numbers on the diagnostic table.
- 5:
If the cause of the DTC is not found and corrected, refer to Fuel System Diagnosis for a possible fuel related condition.
- 6:
On KL6 equipped vehicles, an EVAP canister that is saturated will cause a rich condition. If the condition is not found, a worn cam, worn intake or exhaust valves, or other engine mechanical failure may be the cause of the DTC.
DTC P0172 or P0175
| Step |
Action |
Values |
Yes |
No |
| 1 |
Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls? |
- |
Go to Step 2 |
Go to Diagnostic System Check - Alternative Fuels (Engine Controls) |
| 2 |
IMPORTANT:
If any DTCs other than P0172 or P0175 are set, refer to those DTCs before continuing.
- Install scan tool.
- Start and idle the engine at the normal operating temperature in Closed Loop.
- Record the long term fuel trim data.
- Turn OFF the engine.
- Turn ON ignition, with the engine OFF.
- Review the Freeze Frame/Failure Records, and record the displayed data for this DTC.
Does the scan tool indicate that the long term fuel trim is less than the specified value? |
-15% |
Go to Step 3 |
Go to Diagnostic Aids |
| 3 |
- Operate engine at idle.
- Observe HO2S parameters with a scan tool.
Does the scan tool indicate that the values are within the specified range and fluctuating? |
200-800 mV |
Go to Step 4 |
Go to Step 5 |
| 4 |
- Turn OFF the engine.
- Visually and physically inspect the following items:
- The evaporative emission (EVAP) lines and components, if equipped, for damage or blockage. Refer to
Evaporative Emissions (EVAP) Hose Routing Diagram
in Engine Controls in the C/K Pickup Service Manual.
- The inlet screen of the mass air flow (MAF) sensor for blockage.
- The vacuum hoses for splits, kinks, and proper connections. Refer to the Underhood Emission Hose Routing label.
- The air intake duct for being collapsed or restricted.
- The air filter for being dirty or restricted.
- Check for objects blocking the throttle body.
Did you find and correct the condition? |
- |
Go to Step 7 |
Go to Step 6 |
| 5 |
- Turn OFF the engine.
- Inspect the heated oxygen sensor (HO2S) for proper installation.
- Inspect to ensure that the electrical connectors and the wires are secure and not contacting the exhaust system.
- Test for continuity between the signal circuit and the low reference circuit. Refer to
Circuit Testing
and
Wiring Repairs
in Wiring Systems in the C/K Pickup Service Manual.
Did you find and correct the condition? |
- |
Go to Step 7 |
Go to
Fuel System Diagnosis
in Engine Controls in the C/K Pickup Service Manual |
| 6 |
Inspect for the following:
- Excessive fuel in the crankcase (KL6 only).
- Proper operation of the gasoline fuel pressure regulator (KL6 only). Refer to
Fuel System Diagnosis
in Engine Controls in the C/K Pickup Service Manual.
- All compressed natural gas (CNG) fuel injectors are functioning properly. Refer to Fuel Injector Coil Test
.
- All gasoline fuel injectors are functioning properly. Refer to
Fuel Injector Coil Test
in Engine Controls in the C/K Pickup Service Manual.
Did you find and correct the condition? |
- |
Go to Step 7 |
Go to
Symptoms - Engine Mechanical
in Engine Mechanical in the C/K Pickup Service Manual |
| 7 |
IMPORTANT:
After repairs, use the scan tool Fuel Trim Reset function in order to reset the Long Term Fuel Trim.
- Clear the DTCs with a scan tool.
- Turn OFF the ignition for 30 seconds.
- Start the engine.
- Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition? |
- |
Go to Step 2 |
Go to Step 8 |
| 8 |
Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed? |
- |
Go to Diagnostic Trouble Code (DTC) List |
System OK |