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DTC P0171, P0172, P2187, or P2188 (LLU)

DTC P0171, P0172, P2187, or P2188 (LLU)

Diagnostic Instructions


• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• Diagnostic Procedure Instructions provides an overview of each diagnostic category.


DTC Descriptors

DTC P0171 00

Fuel Trim System Lean

DTC P0172 00

Fuel Trim System Rich

DTC P2187 00

Fuel Trim System Lean at Idle

DTC P2188 00

Fuel Trim System Rich at Idle

Circuit/System Description

The engine control module (ECM) controls the air/fuel metering system by closed loop control in order to give the best possible combination of driveability, fuel economy, and emissions control. The ECM monitors the signal voltage for the heated oxygen sensor (HO2S) and adjusts the fuel supply based on the signal voltage while working in closed loop. A change made to the fuel delivery changes the long and short term fuel trim values. The short term fuel trim values change rapidly in response to the heated oxygen sensor signal voltages. These changes fine tune the engine fueling. The long term fuel trim values change in response to trends in the short term fuel trim. The long term fuel trim makes coarse adjustments to fueling in order to recenter and restore control to short term fuel trim. The ideal fuel trim values are around 0%. A positive fuel trim value indicates that the ECM is adding fuel in order to compensate for a lean condition. A negative fuel trim value indicates that the ECM is reducing the amount of fuel in order to compensate for a rich condition. The fuel trim cells are based on the engine speed and load.

Conditions for Running the DTC


• DTCs P0031 00, P0032 00, P0112 00, P0113 00, P0116 00, P0117 00, P0118 00, P0122 00, P0123 00, P0131 00, P0132 00, P0133 00, P0134 00, P0135 00, P0201 00, P0202 00, P0203 00, P0204 00, P0261 00, P0262 00, P0264 00, P0265 00, P0267 00, P0268 00, P0270 00, P0271 00, P0300 00, P0313 00, P0335 00, P0336 00, P0458 00, P0459 00, P0562 00, and P0563 00 are not set.

• The fuel system is in Closed Loop.

• The engine speed is between 1 400-4 000 RPM

• The engine coolant temperature (ECT) is between 70-115°C (158-239°F).

• The intake air temperature (IAT) sensor is between -40 to +120°C (-40 to +248°F).

• The throttle position is between 0-95%.

• The manifold absolute pressure (MAP) is between 25-99.7 kPa (3.6-14.46 PSI).

• The barometric pressure (BARO) is greater than 72 kPa (10.44 PSI).

• The engine mass air flow (MAF) is between 1.5-45 g/s.

• The ignition voltage is greater than 11 V.

• The DTCs run continuously when the above conditions are met.


Conditions for Setting the DTC

P0171 00

The average long term fuel trim weighted average is greater then a calibrated value.

P0172 00

The average long term fuel trim weighted average is less then a calibrated value.

P2187 00

The average long term fuel trim cell values at idle, cruise, or during acceleration are greater than a calibrated value.

P2188 00

The average long term fuel trim cell values at idle, cruise, or during acceleration are less than a calibrated value.

Action Taken When the DTC Sets

DTCs P0171 00, P0172 00, P2187 00, P2188 00 are type B DTCs

Conditions for Clearing the DTC

DTCs P0171 00, P0172 00, P2187 00, P2188 00 are type B DTCs

Diagnostic Aids


• The system will become lean if a fuel injector is not supplying enough fuel.

• A lean condition may be present during high fuel demand due to a fuel pump that does not deliver enough fuel, a plugged fuel filter, or a restricted fuel pipe.

• The system will become rich if a fuel injector is supplying too much fuel.

• Review the freeze frame/failure records with a scan tool.


Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference


• Circuit Testing

• Connector Repairs

• Testing for Intermittent Conditions and Poor Connections

• Wiring Repairs


DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Note

Disregard any transmission symptoms, antilock brake system (ABS) indicators, and traction control system indicators until any fuel trim faults are repaired. A fuel trim fault may cause default actions as illumination of the antilock brake system (ABS), and traction control system indicators.



1. Engine running, observe the DTC information with a scan tool. Verify that other DTCs are not set.

2. If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .

3. Ignition ON, observe the scan tool MAP sensor pressure parameter and compare the reading on the scan tool to the barometric pressure table. Refer to Altitude Versus Barometric Pressure .

4. If the MAP sensor pressure is not within the range specified for your altitude, refer DTC P2279 (LLU) .

5. Engine running, observe the scan tool MAF Sensor parameter. The MAF Sensor parameter should be between 2-6 g/s at idle.

6. If the MAF Sensor parameter is not between 2-6 g/s at idle, refer to DTC P0100-P0103 (LLU) .

7. Engine running, observe the scan tool Throttle Position sensor percentage parameter. The reading should be less than 10%.

8. If greater than the specified range, refer to DTC P0121-P0123, P0221-P0223, or P2135 (LLU) .

9. Check the scan tool HO2S sensor 1 voltage parameter. The value should vary between 200 mV and 800 mV.

10. If not within the specified range, refer to DTC P0130-P0134 (LLU) .

11. Engine at normal operating temperature, observe the scan tool Long Term Fuel Trim parameter. The reading should be between -5 to +5%.

12. Drive the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that you have noted from the freeze frame/failure records data.


Circuit/System Testing

Note

You must perform the circuit/system verification before proceeding with circuit/system testing.



1. Verify none of the following conditions exist:

• Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

• Splits, kinks, or improper connections at the vacuum hoses

• The fuel system is operating lean or rich. Refer to Fuel System Diagnosis .

• The fuel injectors are operating lean or rich. Refer to Fuel Injector Diagnosis .

• Leaks in the air induction system between the turbocharger outlet and the throttle body inlet, including the air cooler

• Missing, restricted, or leaking exhaust components-Refer to Symptoms - Engine Exhaust .

• Vacuum leaks at the intake manifold, throttle body, and injector O-rings

• Leaking crankcase ventilation system

• The air intake duct for being collapsed or restricted possibly by a restricted air filter

• Excessive fuel in the crankcase

• The incorrect operation of the evaporative emissions control system

2. If all conditions test normal, test the engine for a mechanical condition. Refer to Symptoms - Engine Mechanical .


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.