ISUZU 4JJ1 Engine Construction P0112 Intake Air Temperature Circuit Low Input

The intake air temperature sensor is installed between the air cleaner and the turbocharger. The intake air temperature sensor is a variable resistor and measures the temperature of the intake air flowing into the engine. This sensor has a signal circuit and a GND circuit which are connected to the ECM. The sensor resistance is high when the intake air temperature is low, and the sensor resistance decreases as the intake air temperature increases. The ECM detects a high voltage when the sensor resistance is high, and a low voltage when the sensor resistance is low. If the ECM detects an excessively low signal voltage, the DTC is set.

Condition for setting the DTC

Preconditions

The ignition switch is ON. ・DTCs P060B, P0651, and P160B are not set.

Setting conditions

The ECM detects that the intake air temperature sensor signal voltage is 0.1 V or less for 5 seconds.

Action taken when DTC sets

・Failure is indicated* in the monitor on the machine, or the diagnostic light illuminates.

Note: *Depending on the machine manufacturer, a failure may not be indicated.

・The ECM substitutes a default intake air temperature value. ・The ECM limits the fuel injection quantity.

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ISUZU E-IDSS 2024 2019 Engine Diagnostic Service System Free Download

ISUZU IDSS MX2-T Diagnostic Tool

 

 

P0112 Diagnostics

Prioritized DTC check

Connect a trouble diagnosis scan tool.

Turn OFF the ignition switch for 30 seconds or more.

Turn ON the ignition switch.

Observe the DTC information with a trouble diagnosis scan tool. Is DTC P0651 set?

Yes

Go to DTC P0651 diagnosis.

No

⇒Go to Intake air temperature sensor signal voltage check.

 

Intake air temperature sensor signal voltage check

Observe “Intake air temperature sensor” display on the trouble diagnosis scan tool. Is “Intake air temperature sensor” display less than or equal to the specified value?

values： 0.1 V

Yes

⇒Go to Intake air temperature sensor signal output voltage check.

No

Go to Intermittent conditions of engine.

 

Intake air temperature sensor signal output voltage check

Turn OFF the ignition switch.

Disconnect the intake air temperature sensor harness connector.

Turn ON the ignition switch.

Observe the “Intake air temperature sensor” display on the trouble diagnosis scan tool. Is the “Intake air temperature sensor” display more than or equal to the specified value?

values： 4.5 V

Yes

Replace the intake air temperature sensor.

⇒Go to Repair verification.

No

⇒Go to Inspection for short to ground in intake air temperature sensor signal circuit.

 

Inspection for short to ground in intake air temperature sensor signal circuit

Inspect the signal circuit between the ECM and the intake air temperature sensor for a short to ground or a short to the GND circuit. Is the result normal?

Yes

⇒Go to ECM harness connector inspection.

No

Repair the circuit as necessary.

⇒Go to Repair verification.

 

ECM harness connector inspection

Inspect for poor connections at the ECM harness connector. Is the connection status normal?

Yes

⇒Go to ECM replacement.

No

Repair the connections as necessary.

⇒Go to Repair verification.

 

ECM replacement

Note: Perform programming after replacing the ECM.

Procedure completion

⇒Go to Repair verification.

 

Repair verification

Clear the DTC with a trouble diagnosis scan tool.

Turn OFF the ignition switch for 30 seconds or more.

Start the engine.

Perform a test-run under the conditions for running the DTC.

Observe the DTC information with a trouble diagnosis scan tool. A DTC should not be set.

More repair cases for ISUZU engine,please refer to:ISUZU Engine Trouble Repair