Isuzu KB P190. Manual - part 865

Engine Management – V6 – Diagnostics 

Page 6C1-2–182 

 

• 

The APP sensor 1 signal voltage increases from 1 V at rest position to greater than 4 V when the accelerator 
pedal is fully depressed. 

• 

The APP sensor 2 signal voltage increases from 0.5 V at rest position to greater than 2 V when the accelerator 
pedal is fully depressed. 

The ECM monitors and evaluates the APP sensors signal voltage along with other sensor inputs to determine the 
desired throttle opening. An APP sensor circuit DTC sets if the signal voltage of the APP sensor is outside the 
predetermined range. 

Conditions for Running the DTC 

DTC P2122, P2123, P2127, P2128 and P2138 runs continuously once the following conditions are met: 

• 

The ignition is switched on. 

• 

The ignition voltage is greater than 7 V. 

Conditions for Setting the DTC 

DTC P2122 

The ECM determines the APP sensor 1 signal voltage is less than 0.84 V. 

DTC P2123 

The ECM determines the APP sensor 1 signal voltage is greater than 4.82 V. 

DTC P2127 

The ECM determines the APP sensor 2 signal voltage is less than 0.66 V. 

DTC P2128 

The ECM determines the APP sensor 2 signal voltage is greater than 4.82 V. 

DTC P2138 

The ECM detects the difference between the APP sensor 1 and sensor 2 signal voltage is greater than the 
predetermined value. 

Conditions for Clearing DTC 

The APP sensor circuit DTCs are Type ‘A’ DTCs. Refer to 1.4  Diagnostic Trouble Codes in this Section, for action 
taken when a Type ‘A’ DTC sets and conditions for clearing Type ‘A’ DTCs. 

Additional Information 

• 

Refer to 6C1-1 Engine Management – V6 – General Information for details of the APP sensor operation. 

• 

For an intermittent fault condition, refer to 5.2 

Intermittent Fault Conditions in this Section. 

• 

Since fault condition in a wiring connector may trigger DTCs, always test the connectors related to this diagnostic 
procedure for shorted terminals or poor wiring connection before replacing any component. Refer to 8A Electrical - 
Body and Chassis for information on electrical fault diagnosis. 

• 

To assist diagnosis, refer to 3 

Wiring Diagrams and Connector Charts in this Section, for the system wiring 

diagram and connector charts. 

Test Description 

The following numbers refer to the step numbers in the diagnostic table: 

2 

Tests the APP sensor internal circuits throughout its range of motion. If the DTC fails while performing this test, 
there is an internal fault condition in the APP sensor internal circuitry. 

5 

Measures the integrity of the TP sensor low reference circuit. Removal of the ECM Fuse 29 enables the ECM to 
power down completely prior to the test procedure. 

Engine Management – V6 – Diagnostics 

Page 6C1-2–183 

 

DTC P2122, P2123, P2127, P2128 or P2138 Diagnostic Table  

Step Action 

Yes 

No 

1 

Has the Diagnostic System Check been performed? 

Go to Step 2 

Refer to 

4.4 Diagnostic 
System Check in 

this Section 

2 

1 

Switch off the ignition for 30 seconds. 

2 

Start the engine. 

3 

Quickly depress the accelerator pedal to wide-open throttle then 
release pedal. Repeat this procedure several times or operate 
the vehicle within the conditions for running the DTC. 

4 

Using Tech 2, select the DTC display function. 

Does DTC P2122, P2123, P2127, P2128 or P2138 fail this ignition 
cycle? 

Go to Step 3 

Refer to Additional 

Information in this 

DTC 

3 

1 

Disconnect the APP sensor wiring connector. 

2 

Switch on the ignition with the engine not running. 

3 

Using a digital multimeter, measure the voltage between the 5 V 
reference circuit of the appropriate APP sensor and the ECM 
housing. 

Does the multimeter display 4.8 – 5.2 V? 

Go to Step 4 

Go to Step 6 

4 

1 

Connect a 3 A fused jumper wire between the 5 V reference 
circuit and the signal circuit of the appropriate APP sensor. 

2 

Switch on the ignition with the engine not running. 

3 

Using Tech 2, observe the voltage parameter appropriate APP 
sensor. 

Does Tech 2 display 4.8 – 5.2 V? 

Go to Step 5 

Go to Step 7 

5 

1 

Switch off the ignition. 

2 

Remove ECM / TCM Fuse 29 from the engine compartment 
fuse and relay panel assembly. 

3 

Using a DMM, measure the resistance between the appropriate 
TP sensor low reference circuit and the ECM housing. 

N O T E  

Install the ECM Fuse 29 to the engine compartment fuse 
and relay panel assembly after completing this test. 

Does the multimeter display 5 

Ω? 

Go to Step 9 

Go to Step 8 

6 

Test the 5 V reference circuit of the appropriate APP sensor for a high 
resistance, open circuit, short to ground or short to voltage fault 
condition. Refer to 8A Electrical - Body and Chassis for information on 
electrical fault diagnosis. 

Was any fault found and rectified? 

Go to Step 11 

Go to Step 10 

7 

Test the signal circuit of the appropriate APP sensor for a high 
resistance, open circuit, short to ground or short to voltage fault 
condition. Refer to 8A Electrical - Body and Chassis for information on 
electrical fault diagnosis. 

Was any fault found and rectified? 

Go to Step 11 

Go to Step 10 

8 

Test the low reference circuit of the appropriate APP sensor for a high 
resistance or an open circuit fault condition. Refer to 8A Electrical - 
Body and Chassis for information on electrical fault diagnosis. 

Was any fault found and rectified? 

Go to Step 11 

Go to Step 10 

Engine Management – V6 – Diagnostics 

Page 6C1-2–184 

 

Step Action 

Yes 

No 

9 

Replace the accelerator pedal assembly. Refer to 6C1-3 Engine 
Management – V6 – Service Operations. 

Was the repair completed? 

Go to Step 11 

— 

10  Replace the ECM. Refer to 6C1-3 Engine Management – V6 – 

Service Operations. 

Was the repair completed? 

Go to Step 11 

— 

11  1 

Using Tech 2, clear the DTCs. 

2 

Switch off the ignition for 30 seconds. 

3 

Start the engine. 

4 

Operate the vehicle within the conditions for running the DTC. 

Does any of the APP Sensor Circuit DTCs fail this ignition cycle? 

Go to Step 2 

Go to Step 12 

12  Using Tech 2, select the DTC display function. 

Does Tech 2 display any DTCs? 

Go to the 

appropriate DTC 

Table in this Section 

System OK 

When all diagnosis and repairs are completed, check the system for correct operation. 

7.51  DTC P2177 or P2179 

DTC Descriptors 

This diagnostic procedure supports the following DTCs: 

• 

DTC P2177 Fuel Trim System Lean at Cruise or Accel Bank 1  

• 

DTC P2179 Fuel Trim System Lean at Cruise or Accel Bank 2  

Circuit Description 

The engine control module (ECM) controls the air / fuel metering system to provide the best possible combination of 
driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open and Closed Loop. 
During Open Loop, the ECM determines fuel delivery based on sensor signals without heated oxygen sensor (HO2S) 
input. During Closed Loop, the HO2S inputs are added and used by the ECM to calculate short and long term fuel trim 
fuel delivery adjustments. If the HO2S indicate  a lean condition, fuel trim values will be above 0 percent. If the HO2S 
indicate a rich condition, fuel trim values will be below 0 percent. Short term fuel trim values change rapidly in response 
to the HO2S signals. Long term fuel trim makes coarse adjustments to maintain an air / fuel ratio of 14.7:1. If the ECM 
detects an excessively lean condition, this DTC sets. 

Conditions for Running the DTC 

• 

Before the ECM can report DTC P2177 or P2179 failed, DTCs P0101, P0121, P0122, P0123, P0133, P0153, 
P0221, P0222, P0223, P0336, P0338, P0443, P0458, P0459, P0461, P0462, P0463, P2066, P2067, and P2068 
must run and pass.  

• 

The fuel system is in closed loop.  

• 

The long fuel trim is active.  

• 

The engine coolant temperature (ECT) is more than 60° C. 

• 

The evaporative emission (EVAP) canister purge solenoid valve is not enabled.  

• 

The intake air temperature (IAT) is less than 60° C.  

• 

The fuel level is more than 11.6 percent.  

• 

The amount of air flow into the engine is more than 7,000 grams.  

• 

DTC P2177 and P2179 runs continuously once the above conditions are met for at least 300 seconds.  

Engine Management – V6 – Diagnostics 

Page 6C1-2–185 

 

Conditions for Setting the DTC 

• 

The Total Fuel Trim Avg. is more than 23 percent.  

• 

The condition exists for 4 seconds.  

Action Taken When the DTC Sets 

• 

The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that 
the diagnostic runs and fails.  

• 

The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic 
fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the 
second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. 
The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.  

Conditions for Clearing the MIL/DTC 

• 

The control module turns OFF the malfunction indicator lamp (MIL) after four consecutive ignition cycles that the 
diagnostic runs and does not fail.  

• 

A current DTC, Last Test Failed, clears when the diagnostic runs and passes.  

• 

A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission 
related diagnostic.  

• 

Use Tech 2 to clear the MIL and the DTC.  

Additional Information 

• 

A fuel system delivery condition causes this DTC to set. Thoroughly inspect all items that cause a lean condition.  

• 

Any un-metered air into the engine causes this DTC to set. Thoroughly inspect all areas of the engine for vacuum 
leaks.  

• 

For an intermittent fault condition, refer to 5.2 

Intermittent Fault Conditions in this Section. 

• 

To assist diagnosis, refer to 3 

Wiring Diagrams and Connector Charts in this Section, for the system wiring 

diagram and connector charts. 

Test Description 

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

2 

This step determines if there is a current condition.  

4 

If DTC P2177 and P2179 are set at the same time, this indicates that both banks of the engine are operating lean. 
Inspect for items that would cause both banks of the engine to operate lean. 

5 

Disconnecting the mass air flow (MAF) sensor determines if the MAF sensor signal is skewed. If the Short Term 
FT parameter changes more than the specified value, there is a condition with the MAF sensor. A MAF sensor 
condition can cause this DTC without setting a MAF DTC. If there is a MAF sensor condition, the MAF sensor 
parameters will appear to be within range.  

6 

A vacuum leak causes DTC P2177 and P2179 to set at the same time. Inspect all areas of the engine for a 
vacuum leak. Also inspect the PCV valve for being the correct one for this application. Make sure that the engine 
oil fill cap is in place and that it is tight. Verify that the engine oil dip stick is fully seated. 

DTC P2177 or P2179 Diagnostic Table 

Step Action  Value(s) 

Yes 

No 

1 

Has the Diagnostic System Check been completed? 

— 

Go to Step 2 

Refer to  

4.4 Diagnostic 

System Check in this 

Section