2001 Chevrolet/Geo Camaro  

DTC P0171 or P0174

Circuit Description

The powertrain control module (PCM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy and emission control. Fuel delivery is controlled differently during Open and Closed Loop. During Open Loop the PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During Closed Loop the PCM adds oxygen sensor inputs to calculate Short and Long Term fuel trim (fuel delivery adjustments). If the oxygen sensors indicate a lean condition, fuel trim values will be above 0 percent . If the oxygen sensors (O2S) indicate a rich condition, fuel trim values will be below 0 percent. Short Term fuel trim values change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. Long Term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. If the PCM detects an excessively lean condition, this diagnostic trouble code (DTC) will set.

Conditions for Running the DTC
Conditions for Setting the DTC
Action Taken When the DTC Sets
Conditions for Clearing the MIL/DTC
Diagnostic Aids
Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. If conditions were not corrected, refer to Fuel System Diagnostics for a possible fuel problem.

  2. If conditions were not corrected, a worn cam, worn intake or exhaust valves, or other the engine mechanical failures may be at fault.

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Important

If any DTCs are set, other than P0171, refer to those DTCs before continuing.

  1. Install the scan tool.
  2. Start and idle the engine at normal operating temperature in Closed Loop.
  3. Record the Long Term fuel trim data.
  4. Turn OFF the engine.
  5. Turn ON the ignition, with the engine OFF.
  6. Review the Freeze Frame and Failure Records, and record displayed data for this DTC.

Does the scan tool indicate that the Long Term fuel trim is greater than the specified value?

23%

Go to Step 3

Go to Diagnostic Aids

3
  1. Operate engine at idle.
  2. Using the scan tool observe the HO2S parameters.

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
  1. Turn OFF engine.
  2. Visually and physically inspect the following items:

Did you find and correct the condition?

--

Go to Step 7

Go to Step 6

5
  1. Turn OFF engine.
  2. Check the HO2S for proper installation.
  3. Check to ensure electrical connectors and wires are secured and not contacting the exhaust system.
  4. Check for a short between the signal circuit and the low reference circuit.

Did you find and correct the condition?

--

Go to Step 7

Go to Fuel System Diagnosis

6
  1. Operate the engine at idle.
  2. Check for missing, loose, or leaking exhaust components, forward of the HO2S.
  3. Check for vacuum leaks at the intake manifold, throttle body and injector O-rings.
  4. Check the air induction system and air intake ducts for leaks.
  5. Check the secondary air injection (AIR) system for leaks, improper air delivery, shut off valve not closing.
  6. Check crankcase ventilation system for leaks--Refer to Crankcase Ventilation System Inspection/Diagnosis .

Did you find and correct the condition?

--

Go to Step 7

Go to Symptoms - Engine Mechanical

7

Important

After repairs, use scan tool Fuel Trim Reset function in order to reset the Long Term Fuel.

  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 8

Go to Step 2

8

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK