DTC P2178

Fuel system too rich at off idle

DETECTION CONDITION

• PCM monitors short term fuel trim (SHRTFT), long term fuel trim (LONGFT) during closed loop fuel control at off-idle. If the LONGFT and the sum total of these fuel trims exceed preprogrammed criteria. PCM determines that fuel system is too rich at off-idle.

Diagnostic support note

• This is a continuous monitor. (Fuel system)

• The MIL illuminates if the PCM detects the above malfunctioning condition in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM.

• PENDING CODE is available if the PCM detects the above malfunction conditions during the first drive cycle.

• FREEZE FRAME DATA is available.

• The DTC is stored in the PCM memory.

POSSIBLE CAUSE

• Misfire

• Front HO2S deterioration

• Front HO2S heater malfunction

• MAF sensor malfunction

• Pressure regulator (built-in fuel injection pump) malfunction

• Fuel pump malfunction

• EGR valve improper operation

• Purge solenoid valve improper operation

• Purge solenoid valve malfunction (stuck open)

• Purge solenoid hoses improper connection

• PCV valve malfunction

• Variable valve timing control system improper operation

• PCM malfunction

STEP

INSPECTION

ACTION

1

• Have FREEZE FRAME DATA and DIAGNOSTIC MONITORING TEST RESULTS (Fuel system related) been recorded?

Yes

Go to the next step.

No

Record the FREEZE FRAME DATA and DIAGNOSTIC MONITORING TEST RESULTS on the repair order, then go to the next step.

2

• Verify related Service Bulletins and/or on-line repair information availability.

• Is any related repair information available?

Yes

Perform repair or diagnosis according to the available repair information.

• If the vehicle is not repaired, go to the next step.

No

Go to the next step.

3

• Turn the ignition switch off, then to the ON position (Engine off).

• Verify related pending code or stored DTCs.

• Is other DTC present?

Yes

If misfire DTC is present, go to Step 8.

If other DTC is present, go to applicable DTC inspection.

(See DTC TABLE [LF].)

No

If driveability concern is present, go to Step 8.

If not, go to the next step.

4

• Is DTC P2178 on FREEZE FRAME DATA?

Yes

Go to the next step.

No

Go to troubleshooting procedures for DTC on FREEZE FRAME DATA.

5

• Access APP1, APP2, ECT, MAF, TP and VSS PIDs using M-MDS.

• Is there any signal that is far out of specification when the ignition switch is at the ON position and the engine runs?

Yes

Inspect the sensor and excessive resistance in related wiring harnesses.

Repair if necessary.

Then go to Step 15.

No

Go to the next step.

6

• Inspect the same PIDs as Step 5 while simulating FREEZE FRAME DATA condition.

• Is there any signal which causes drastic changes?

Yes

Inspect the sensor and related wiring harnesses, repair or replace it.

Then go to Step 15.

No

Go to the next step.

7

• Inspect the front HO2S

  (See FRONT HEATED OXYGEN SENSOR (HO2S) INSPECTION [LF].)

• Is HO2S normal?

Yes

Go to the next step.

No

Visually inspect for any gas leakage between the exhaust manifold and the front HO2S.

Then go to Step 15.

8

• Connect the M-MDS to the DLC-2

• Start the engine.

• Access the MAF PID.

• Verify that the MAF PID changes quickly according to engine speed.

• Is the PID normal?

Yes

Go to the next step.

No

Replace the MAF/IAT sensor, then go to Step 15.

(SeeMASS AIR FLOW (MAF)/INTAKE AIR TEMPERATURE (IAT) SENSOR REMOVAL/INSTALLATION [LF].)

9

• Perform Purge Control System Inspection.

  (See ENGINE CONTROL SYSTEM OPERATION INSPECTION [LF].)

• Does purge control system work properly?

Yes

Go to the next step.

No

Repair or replace the malfunctioning part according to inspection result, then go to Step 15.

10

• Inspect the PCV valve operation.

  (See POSITIVE CRANKCASE VENTILATION (PCV) VALVE INSPECTION [LF].)

• Is the PCV valve normal?

Yes

Go to the next step.

No

Replace the PCV valve, then go to Step 15.

11

• Perform EGR Control System Inspection.

  (See ENGINE CONTROL SYSTEM OPERATION INSPECTION [LF].)

• Does the EGR control system work properly?

Yes

Go to the next step.

No

Repair or replace the malfunctioning part according to inspection result, then go to Step 15.

12

• Turn the ignition switch off.

• Inspect the fuel line pressure.

  (See FUEL LINE PRESSURE INSPECTION [LF].)

• Is the fuel line pressure normal?

Yes

Go to the next step.

No

If the fuel pressure is too high, replace fuel pump unit, then go to Step 15.

If the fuel line pressure is low, go to the next step.

13

• Visually inspect the fuel line for any leakage.

• Is fuel leakage found?

Yes

Replace suspected fuel line, then go to the next step.

No

Inspect for foreign materials or stain inside fuel filter (low-pressure).

If for foreign materials or stain inside fuel filter (low-pressure), clean off the fuel tank and filter.

Then go to the next step.

14

• Inspect variable valve timing control system operation.

  (See ENGINE CONTROL SYSTEM OPERATION INSPECTION [LF].)

• Does variable valve timing control system work properly?

Yes

Go to the next step.

No

Repair or replace the malfunctioning part according to inspection results, then go to the next step.

15

• Make sure to reconnect all disconnected connectors.

• Clear the DTC from the PCM memory using the M-MDS.

• Perform the KOER self-test (using M-MDS) or the HO2S heater, HO2S, and TWC Repair Verification Drive Mode (not using M-MDS).

  (See KOEO/KOER SELF TEST [LF].)

  (See OBD-II DRIVE MODE [LF].)

• Is the PENDING CODE for this DTC present?

Yes

Replace the PCM, then go to the next step.

(See PCM REMOVAL/INSTALLATION [LF].)

No

Go to the next step.

16

• Perform “AFTER REPAIR PROCEDURE”.

  (See AFTER REPAIR PROCEDURE [LF].)

• Is there any DTC present?

Yes

Go to the applicable DTC inspection.

(See DTC TABLE [LF].)

No

Troubleshooting completed.