Isuzu KB P190. Manual - part 839

Engine Management – V6 – Diagnostics 

Page 6C1-2–78 

 

Step Action 

Yes 

No 

10  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 ECT sensor DTCs fail this ignition cycle? 

Go to Step 2 

Go to Step 11 

11  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. 

7.9 

DTC P0121, P0122, P0123, P0221, 
P0222,or P0223 

DTC Descriptors 

This diagnostic procedure supports the following DTCs: 

• 

DTC P0121 – Throttle Position Sensor 1 Circuit Range / Performance 

• 

DTC P0122 – Throttle Position Sensor 1 Circuit Low Voltage 

• 

DTC P0123 – Throttle Position Sensor 1 Circuit High Voltage 

• 

DTC P0221 – Throttle Position Sensor 2 Circuit Range / Performance 

• 

DTC P0222 – Throttle Position Sensor 2 Circuit Low Voltage 

• 

DTC P0223 – Throttle Position Sensor 2 Circuit High Voltage 

Circuit Description 

The ECM applies 5 V to the throttle position (TP) sensor 1 through the 5 V reference circuit and the ground through the 
low reference circuit. TP sensor 1 and TP sensor 2 share common 5 V reference circuit and low reference circuit. 

The TP sensor 1 and TP sensor 2 have individual signal circuits with opposite functionality. These signal circuits provide 
the ECM with a signal voltage that is proportional to the throttle plate movement. 

• 

The TP sensor 1 signal voltage is less than 1 V when the throttle plate is in closed position, which increases to 
greater than 4 V when the throttle plate is moved to wide-open throttle. 

• 

The TP sensor 2 signal voltage is greater than 4 V when the throttle plate is in closed position, which decreases to 
less than 1 V when the throttle plate is moved to wide-open throttle. 

The ECM monitors and compares the TP sensor 1 signal voltage to the TP sensor signal voltage 2. In addition, the ECM 
compares the TP sensor signal to the MAF sensor signal to determine a calculated TP sensor signal. 

A TP sensor DTC sets if the ECM detects a fault condition in the TP sensor signal output. 

Conditions for Running the DTC 

DTC P0121 runs continuously once the following conditions are met: 

• 

The ignition voltage is greater than 7 V. 

• 

The TP sensor 1 signal voltage is 0.17 – 4.6 V. 

DTC P0122, P0123, P0222 and P0223 runs continuously once the following conditions are met: 

• 

The ignition voltage is greater than 7 V. 

• 

The ignition is switched on. 

DTC P0221 runs continuously once the following conditions are met: 

• 

The battery voltage is greater than 7 V. 

Engine Management – V6 – Diagnostics 

Page 6C1-2–79 

 

• 

The TP sensor 2 signal voltage is 0.15 – 4.8 V. 

DTC P0222 runs continuously once the following conditions are met: 

• 

The battery voltage is greater than 7 V. 

• 

The ignition is switched on. 

Conditions for Setting the DTC 

DTC P0121 

The following conditions exist: 

• 

The TP sensor 1 signal voltage and the TP sensor 2 signal voltage have a difference of greater than 9 percent. 

• 

The TP sensor signal voltage has a difference of greater than 9 percent from the calculated TP sensor signal 
voltage. 

DTC P0122 

The ECM detects the TP sensor 1 signal voltage is less than 0.18 volt. 

DTC P0123 

The ECM detects the TP sensor 1 signal voltage is greater than 4.6 V. 

DTC P0221 

The following conditions exist: 

• 

The TP sensor 2 signal voltage and the TP sensor 1 signal voltage have a difference of greater than 9 percent. 

• 

The TP sensor 2 signal voltage has a difference of greater than 9 percent from the calculated TP sensor signal 
voltage. 

DTC P0222 

The ECM detects the TP sensor 2 signal voltage is less than 0.16 volt. 

DTC P0223 

The ECM detects the TP sensor 2 signal voltage is greater than 4.8 V. 

Conditions for Clearing the DTC 

DTCs P0121, P0122, P0123, P0221, P0222 are P0223 are Type B DTCs. Refer to 1.4 

Diagnostic Trouble Codes in 

this Section, for action taken when a Type B DTC sets and conditions for clearing Type B DTCs. 

Additional Information 

• 

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

• 

The ECM defaults to a reduced power mode if there is a fault condition in the TP sensor circuits for the entire 
ignition cycle, even if the fault condition is corrected. 

• 

For an intermittent fault condition, refer to 5.2 

Intermittent Fault Conditions in this Section. 

• 

The TP sensors share a common 5 V reference circuit, test for a fault condition in the 5 V reference circuit if both 
DTCs P0122 and P0222 are set. 

• 

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. 

Engine Management – V6 – Diagnostics 

Page 6C1-2–80 

 

Test Description 

The following number refers to the step number in the diagnostic table: 

6 

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. 

DTC P0121, P0122, P0123, P0221, P0222 or P0223 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 P0121, P0122, P0123, P0221, P0222 or P0223 fail this 
ignition cycle? 

Go to Step 3 

Refer to Additional 

Information in this 

DTC 

3 

1 

Disconnect the throttle actuator wiring connector. 

2 

Switch on the ignition with the engine not running. 

3 

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

Does the multimeter display 4.8 – 5.2 V? 

Go to Step 4 

Go to Step 7 

4 

1 

Connect a 3 A fused jumper wire between the TP sensor 5 V 
reference circuit and the TP sensor 1 signal circuit. 

2 

Switch on the ignition with the engine not running. 

3 

Using Tech 2, observe the TP sensor 1 voltage parameter. 

Does Tech 2 display 4.8 – 5.2 V? 

Go to Step 5 

Go to Step 8 

5 

1 

Connect a 3 A fused jumper wire between the TP sensor 5 V 
reference circuit and the TP sensor 2 signal circuit. 

2 

Using Tech 2, observe the TP sensor 2 voltage parameter. 

Does Tech 2 display 4.8 – 5.2 V? 

Go to Step 6 

Go to Step 9 

6 

1 

Switch off the ignition. 

2 

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

3 

Using a digital multimeter, measure the resistance between the 
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 the test. 

Does the multimeter display 5 

Ω? 

Go to Step 11 

Go to Step 10 

Engine Management – V6 – Diagnostics 

Page 6C1-2–81 

 

Step Action 

Yes 

No 

7 

N O T E  

TP sensor 1 share the 5 V reference circuit with TP sensor 
2. A fault condition in the TP sensor 5 V reference circuit 
may trigger DTCs on both sensors. 

Test the TP sensor 5 V reference circuit 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 13 

Go to Step 12 

8 

Test the TP sensor 1 signal circuit 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 13 

Go to Step 12 

9 

Test the TP sensor 2 signal circuit 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 13 

Go to Step 12 

10  Test the TP sensor low reference circuit 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 13 

Go to Step 12 

11  Replace the throttle body assembly. Refer to 6C1-3 Engine 

Management – V6 – Service Operations. 

Was the repair completed? 

Go to Step 13 

— 

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

Service Operations. 

Was the repair completed? 

Go to Step 13 

— 

13  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 TP Sensor Circuit DTCs fail this ignition cycle? 

Go to Step 2 

Go to Step 14 

14  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. 

7.10  DTC P0130, P0131, P0132, P0135, P0137, 

P0138, P0140, P0141, P0150 P0151, 
P0152, P0155, P0157, P0158, P0160, 
P0161, P2243, P2247, P2270, P2271, 
P2272, P2273, P2297 or P2298 

DTC Descriptors 

This diagnostic procedure supports the following DTCs: 

• 

DTC P0130 – O2 Sensor Circuit Malfunction (Bank 1, Sensor 1)