P0175
SYMPTOM
P0175 - FUEL SYSTEM 2/1 RICH
WHEN MONITORED
With the engine running in closed loop mode, the ambient/battery temperature above 20 °F and altitude below 8500 ft.
SET CONDITION
If the PCM multiplies short term compensation by long term adaptive and a purge fuel multiplier and the result is below a certain value for 30 seconds over two trips, a freeze frame is stored, the MIL illuminates and a trouble code is stored. Two Trip Fault. Three good trips to turn off the MIL.
POSSIBLE CAUSES
- 02 SENSOR HEATER OPERATION
- EVAP PURGE SOLENOID OPERATION
- 02 SIGNAL CIRCUIT
- 02 RETURN CIRCUIT
- 02 SENSOR
- MAP SENSOR
- ECT SENSOR
- ENGINE MECHANICAL PROBLEM
- FUEL FILTER/PRESSURE REGULATOR (HIGH)
- PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Scan Tool Testing and Procedures
DIAGNOSTIC TEST
1. ACTIVE DTC
Note: Check for contaminates that may have damaged an 02 Sensor: contaminated fuel, unapproved silicone, oil and coolant.
Ignition on, engine not running.
With a scan tool, read DTCs.
Is the DTC active at this time?
Yes>> Go To 2
No>> Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5. Powertrain Verification Test - Ver 5
2. CHECKING FUEL PRESSURE
WARNING: The fuel system is under a constant pressure (even with the engine off). Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be released. Failure to follow these instructions can result in personal injury or death.
Install a fuel pressure gauge to the fuel rail.
Ignition on, engine not running.
With the scan tool, actuate the ASD Fuel System test and observe the fuel pressure gauge.
Note: Fuel pressure specification is 407 kPa ± 34 kPa (59 psi ± 5 psi).
Turn the ignition off.
CAUTION: Stop All Actuations.
Choose a conclusion that best matches your fuel pressure reading.
Within Specification
Go To 3
Above Specification
Replace the fuel filter/pressure regulator. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
3. 02 SENSOR OPERATION
Start the engine.
Allow the engine to reach normal operating temperature.
Note: If one of the 02 Sensors Signal or Return circuit is shorted to ground or voltage, all the other 02 Sensor voltage readings will be affected.
Note: After the repairs have been made, verify proper 02 Sensor operation. If all the 02 Sensor voltage readings have not returned to normal, follow the diagnostic procedure for the remaining 02 Sensors.
With the scan tool, monitor the 2/1 02 Sensor voltage reading.
Is the voltage switching between 2.5 and 3.4 volts?
Yes>> Go To 4
No>> Go To 9
4. 2/1 02 SENSOR HEATER OPERATION
Turn the ignition off.
Note: Wait a minimum of 10 minutes to allow the 02 Sensor to cool down before continuing the test. Allow the 02 Sensor voltage to stabilize at 5.0 volts.
Ignition on, engine not running.
With the scan tool, perform the 2/1 02 Heater Test for each 02 Sensor.
With the scan tool, monitor the 2/1 02 Sensor voltage while performing the Heater test for at least 2 minutes.
Does the voltage stay above 4.5 volts for each Sensor?
Yes>> Replace the 2/1 02 Sensor. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Go To 5
5. MAP SENSOR OPERATION
Turn the ignition off.
Connect a Vacuum Gauge to a Manifold Vacuum source.
Start the engine.
Allow the engine to idle.
Note: If engine will not idle, maintain a constant RPM above idle.
With the scan tool, read the MAP Sensor vacuum value.
Is the scan tool reading within 1" of the Vacuum Gauge reading?
Yes>> Go To 6
No>> Replace the MAP Sensor. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
Note: Remove the vacuum gauge before continuing.
6. ECT SENSOR OPERATION
Note: For this test to be valid, the thermostat must be operating correctly.
Note: This test works best if performed on a cold engine (cold soak).
Ignition on, engine not running.
With the scan tool, read the Engine Coolant Temperature Sensor value. If the engine was allowed to sit overnight (cold soak), the temperature value should be a sensible value that is somewhere close to the ambient temperature.
Note: If engine coolant temperature is above 82 °C (180 °F), allow the engine to cool until 65 °C (150 °F) is reached.
Start the Engine.
During engine warm-up, monitor the Engine Coolant Temperature value. The temp value change should be a smooth transition from start up to normal operating temp 82 °C (180 °F). The value should reach at least 82 °C (180 °F).
Did the ECT value increase smoothly and reach at least 180 °F (82 °C)?
Yes>> Go To 7
No>> Replace the Engine Coolant Temperature Sensor. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
7. EVAP PURGE SOLENOID OPERATION
Turn the ignition off.
Disconnect the hoses at the EVAP Purge Solenoid.
Using a hand vacuum pump, apply 10 in. of vacuum to the EVAP Purge Solenoid vacuum source port on the component side.
Did the EVAP Purge Solenoid hold vacuum?
Yes>> Go To 8
No>> Replace the EVAP Purge Solenoid. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5. Note: Connect the vacuum hoses before continuing.
8. ENGINE MECHANICAL PROBLEM
Check for any of the following conditions/mechanical problems. AIR INDUCTION SYSTEM - must be free from restrictions.
ENGINE VACUUM - must be at least 13 in. in neutral
ENGINE VALVE TIMING - must be within specifications
ENGINE COMPRESSION - must be within specifications
ENGINE EXHAUST SYSTEM - must be free of any restrictions or leaks.
ENGINE PCV SYSTEM - must flow freely
TORQUE CONVERTER STALL SPEED - must be within specifications
POWER BRAKE BOOSTER - no internal vacuum leaks
FUEL - must be free of contamination
FUEL INJECTOR - plugged or restricted injector; control wire not connected to correct injector
Are there any engine mechanical problems?
Yes>> Repair as necessary. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Go To 12
9. 2/102 SENSOR
Ignition on, engine not running.
Disconnect the 2/1 02 Sensor harness connector.
With the scan tool, monitor the 2/1 02 Sensor voltage.
02 Sensor voltage should read 5.0 volts on the scan tool with the connector disconnected.
Connect a jumper wire between the (K43) 02 Sensor 2/1 Signal circuit and the (K902) 02 Upstream Return circuit in the 02 Sensor harness connector.
Note: The voltage should drop from 5.0 volts down to 2.5 volts with the jumper wire connected.
Did the 02 Sensor voltage drop from 5 volts to 2.5 volts when the jumper wire was installed?
Yes>> Replace the 02 Sensor. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Go To 10 Note: Remove the jumper wire before continuing.
10. 02 SENSOR SIGNAL CIRCUIT
WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.
Start the engine.
Measure the voltage on the (K43) 02 Sensor 2/1 Signal circuit in the 02 Sensor harness connector.
Is the voltage above 4.8 volts?
Yes>> Check the (K43) 02 Sensor 2/1 Signal circuit for damage, short to ground, open, or short to voltage. Inspect the 02 Sensor connector and the PCM harness connector. If OK, replace and program the Powertrain Control Module per Service Information. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Go To 11
11. (K902) 02 SENSOR UPSTREAM RETURN CIRCUIT
Engine still running.
Measure the voltage on the (K902) 02 Upstream Return circuit in the 02 Sensor harness connector.
Is the voltage at 2.5 volts?
Yes>> Go To 12
No>> Check the (K902) 02 Upstream Return circuit for damage, short to ground, open, or short to voltage. Inspect the 02 Sensor connector and the PCM harness connector. If OK, replace and program the Powertrain Control Module per Service Information. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
Note: Turn the ignition off before continuing.
12. PCM
Note: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.
Using the schematics as a guide, inspect the wire harness and connectors.
Pay particular attention to all Power and Ground circuits.
Were there any problems found?
Yes>> Repair as necessary. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Replace and program the Powertrain Control Module per Service Information. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.