GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1996 🢒 Blazer - 2WD 🢒 DTC 🢒 DTC P1171 Fuel System Lean During Acceleration

System Description

The PCM's internal circuitry can identify if the vehicle fuel system is capable of supplying adequate amounts of fuel during heavy acceleration (power enrichment). When a power enrichment mode of operation is requested during a Closed Loop operation (by heavy acceleration), the PCM provides additional fuel to the engine. Under these conditions the PCM should detect a rich condition. Whenever this rich exhaust is not detected, a DTC P1171 sets. A plugged fuel filter or restricted fuel line can prevent adequate amounts of fuel from being supplied during power enrichment mode.

Conditions For Setting The DTC
    • The O2S 1 voltage is less than 300 mV for 5 seconds.
    • The O2S 1 operating in a Closed Loop.
    • The fuel Injector BPW is greater than 0.
    • The fuel delivery system is in the power enrichment mode.
    • One or more of the following DTCs are not set; P0131, P0132, P0133, P0134.

Action Taken When the DTC Sets
    • The PCM records the operating conditions at the time the diagnostic fails. The Failure Records buffers stores this information.
    • A history DTC is stored.

Conditions for Clearing the DTC
    • A History DTC clears after 40 consecutive warm up cycles without a fault.
    • Use a scan tool to clear the DTCs.

Diagnostic Aids
    • A restricted fuel filter can supply adequate amounts of fuel at idle, but may not be able to supply enough fuel during heavy acceleration. Water or alcohol in the fuel may cause low O2S 1 voltage during acceleration.
    • Check for faulty or plugged fuel injectors.

Test Description

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

  1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the Freeze Frame Data and the Failure Records on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurs. Refer to this information on the scan tool later.

    2.

  2. When the engine is idling or at a steady cruise, the O2S-1 voltage should vary from approximately 100 mV to 900 mV. During power enrichment mode, more fuel is needed and the O2S-1 voltage should rise above 447 mV.

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Are any component related DTCs set?

--

Go to the Applicable DTC Table

Go to Step 3

3
  1. Check the vehicle for an adequate amount of fuel.
  2. Add fuel to the vehicle's fuel tank, if the tank is almost empty.

Was it necessary to add fuel?

--

Go to Step 5

Go to Step 4

4
  1. Using a scan tool, observe the O2S-1 voltage while running the engine at the specified temperature and RPM.
  2. The O2S-1 voltage should vary from the specified voltage and occasionally toggle above the specified voltage.

Does the O2S-1 toggle?

75° C to 95° C (167° F to 203° F)

1200 RPM

100 to 900 mV

447 mV

Go to Fuel System Pressure Test

Go to DTC P0134 O2S Circuit Insufficient Activity Sensor 1

5
  1. Using the scan tool, clear the DTCs.
  2. Start the Engine.
  3. Allow the engine to idle until the engine reaches the specified temperature.
  4. Operate the vehicle within the conditions for setting this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic ran and passed?

90°-95° C

Go to Step 6

Go to Step 2

6

Check if any additional DTCs are set.

Are any DTCs displayed that have not been diagnosed?

--

Go to the Applicable DTC Table

System OK