SAAB WIS ONLINE

DTC P0171 or P0172

DTC P0171 or P0172

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

Fuel Trim System Lean

DTC P0172

Fuel Trim System Rich

Circuit/System Description

The engine control module (ECM) controls the fuel metering system 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 (FT) values. The short term FT value gets changed rapidly in response to the voltage signals from the HO2S. These changes fine-tune the engine fuel mixture. The long term FT makes coarse adjustments in order to maintain an optimum air/fuel ratio. The ideal FT value is around 0 %. A positive FT value indicates that the ECM is adding fuel in order to compensate for a lean setting. A negative FT value indicates that the ECM is reducing the amount of fuel in order to compensate for a rich condition.

Conditions for Running the DTC


• DTCs P0030, P0053, P0101, P0102, P0103, P0106, P0107, P0108, P0131, P0132, P0133, P0134, P0135, P0178, P0179, P0201-P0204, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0300, P0301-P0304, P0442, P0443, P0446, P0449, P0452, P0453, P0455, P0496, P0506, P0507, P1133, P1248, P1249, P124A, P124B, P2147, P2148, P2150, P2151, P2153, P2154, P2156, P2157, P2269, P2A00 are not set.

• The engine is in Closed Loop status.

• The catalyst monitor intrusive test is not active.

• The post O2 sensor intrusive test is not active.

• The device controls are not active.

• The EVAP tank pull down test is not active.

• The engine coolant temperature (ECT) is between -20 and +150°C (-4 and +302°F).

• The intake air temperature (IAT) is between -20 and +150°C (-4 and +302°F).

• The manifold absolute pressure (MAP) is between 10-255 kPa (1.5-37 PSI).

• The engine speed is between 450-6,500 RPM.

• The mass air flow (MAF) is between 1-512 g/s.

• The barometric pressure (BARO) is more than 70 kPa (10.2 PSI).

• The fuel level is more than 10 percent.

• These DTCs run continuously when the above conditions are met


Conditions for Setting the DTC


• The long term FT weighted average value is more or less than a calibrated value.

• The above condition is present for approximately 3 minutes after the conditions for running the DTC have been met.


Action Taken When the DTC Sets

DTCs P0171 and P0172 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0171 and P0172 are Type B DTCs.

Diagnostic Aids


•
Note

EVAP purge enablement may cause the FT to be momentarily outside the normal range.


The normal Short Term FT parameter should be between +10 percent and -10 percent, with near 0 percent the optimum, with the engine running at operating temperature.

• The Long Term FT parameter should be between +10 percent and -10 percent, with near 0 percent the optimum, with the engine running at operating temperature.

• Certain aftermarket air filters may cause a DTC to set.

• Certain aftermarket air induction systems or modifications to the air induction system may cause a DTC to set.

• Certain aftermarket exhaust system components may cause a DTC to set.


Reference Information

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


1. Verify that other DTCs are not set.

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

3. With the ignition ON and the engine OFF, observe the intake manifold absolute pressure (MAP) sensor parameter. The MAP Sensor pressure should be within the range specified for your altitude. Refer to Altitude Versus Barometric Pressure .

4. If the MAP sensor does not indicate the correct barometric pressure, refer to DTC P0106 .

5. With the engine idling, observe the mass air flow (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 P0101 (LDK With Turbocharger) or DTC P0102 or P0103 (LDK With Turbocharger) .


P0171

Note

EVAP purge enablement may cause the FT to be momentarily outside the normal range.


Allow the engine to reach operating temperature. With the engine running, observe the Long Term FT parameter with a scan tool. The reading should be between 0-20 percent.


• Vacuum hoses for splits, kinks, and improper connections

• Insufficient fuel in the tank

• Low fuel pressure-Refer to Fuel System Diagnosis .

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

• Malfunctioning fuel injectors-Refer to Fuel Injector Solenoid Coil Test .

• Missing, loose, or leaking exhaust components from the HO2S forward-Refer to Symptoms - Engine Exhaust .

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

• The air induction system and the air intake ducts for leaks or for a missing air filter element

• A cracked EVAP canister

• Evaporative pipes obstructed or leaking

• The crankcase ventilation system for leaks-Refer to Crankcase Ventilation System Inspection/Diagnosis (With Turbocharger) .

• The HO2S for improper installation and for electrical wires or connectors that may have contacted the exhaust system

• The HO2S signal circuit open, shorted to ground, or shorted to the low reference circuit

• Malfunctioning engine components-Refer to Symptoms - Engine Mechanical .


P0172

Note

EVAP purge enablement may cause the FT to be momentarily outside the normal range.


Allow the engine to reach operating temperature. With the engine running, observe the Long Term FT parameter with a scan tool. The reading should be between -20 and 0 percent.


• Vacuum hoses for splits, kinks, and improper connections

• The air intake duct for being collapsed or restricted

• The air filter for being dirty or restricted

• Objects blocking the throttle body

• Excessive fuel in the crankcase due to leaking fuel injectors

• The EVAP control system for improper operation

• Excessive fuel pressure-Refer to Fuel System Diagnosis .

• Malfunctioning fuel injectors-Refer to Fuel Injector Solenoid Coil Test .

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

• The HO2S for improper installation and for electrical wires or connectors that may have contacted the exhaust system

• The HO2S signal circuit shorted to voltage

• Malfunctioning engine components-Refer to Symptoms - Engine Mechanical .


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.