Intake Air Temperature (IAT) Sensor

1994 PCED OBDI-A

SECTION 18A: Diesel Diagnosis — 7.3L DI Engine

C: Intake Air Temperature (IAT) Sensor

C1 DIAGNOSTIC TROUBLE CODE (DTC) 152: INDUCE OPPOSITE DTC 151

DTC 152 (IAT) indicates that the corresponding sensor signal is greater than the self-test maximum. The maximum for IAT sensor is 4.59 volts.

Possible causes:

Open in harness.
Worn or damaged connection.
Worn or damaged sensor.
Worn or damaged Powertrain Control Module (PCM).

Key off.
Disconnect suspect temperature sensor.
Connect a jumper wire between the sensor signal circuit and SIG RTN circuit at the temperature sensor vehicle harness connector.
Run Key On Engine Off Self-Test.

Is DTC 151 present?

Yes	No
REPLACE suspect sensor. REMOVE jumper wire. RECONNECT vehicle harness. RERUN Scan Tool Diagnostic Test.	REMOVE jumper wire. GO to C2.

C2 CHECK CONTINUITY OF SENSOR SIGNAL AND SIG RTN CIRCUITS

Key off.
Suspect temperature sensor disconnected.
Disconnect powertrain control module (PCM). Inspect for damaged or pushed-out pins, corrosion, loose wires, etc. Service as necessary.
Install breakout box, leave PCM disconnected.
Measure resistance between sensor signal circuit at the temperature sensor vehicle harness connector Pin B and Test Pin 39 (IAT) at the breakout box.
Measure resistance between SIG RTN circuit at the temperature sensor vehicle harness connector Pin A and Test Pin 91 at the breakout box.

Is each resistance less than 5 ohms?

Yes	No
REPLACE PCM. REMOVE breakout box. RECONNECT all components. RERUN Scan Tool Diagnostic Test.	SERVICE open circuits. REMOVE breakout box. RECONNECT all components. RERUN Scan Tool Diagnostic Test.

C3 DIAGNOSTIC TROUBLE CODE (DTC) 151: INDUCE OPPOSITE CODE 152

DTC 151 (IAT) indicates that the corresponding sensor's signal is less than the Self-Test minimum. The IAT sensor minimum is 0.13 volts.

Possible causes:

Grounded circuit in harness.
Worn or damaged sensor.
Worn or damaged powertrain control module (PCM).
Worn or damaged connection.

Key off.
Disconnect vehicle harness from suspect sensor. Inspect for damaged, corroded, pushed-out pins or loose wires, etc. Service as necessary.
Run Key On Engine Off Self-Test.

Is DTC 152 present?

Yes	No
REPLACE sensor. RECONNECT harness. RERUN Scan Tool Diagnostic Test. GO to C5.	GO to C4.

C4 CHECK TEMPERATURE SENSOR SIGNAL CIRCUIT FOR SHORT TO GROUND

Key off.
Suspect temperature sensor disconnected.
Disconnect powertrain control module (PCM). Inspect for damaged or pushed-out pins, corrosion, loose wires, etc. Service as necessary.
Install breakout box, leave PCM disconnected.
Measure resistance between Test Pin 39 (IAT) and Test Pins 51, 76, 77, 91 and 103.

Is each resistance greater than 10,000 ohms?

Yes	No
REPLACE PCM. REMOVE breakout box. RECONNECT all components. RERUN Scan Tool Diagnostic Test.	SERVICE short circuit. REMOVE breakout box. RECONNECT all components. RERUN Scan Tool Diagnostic Test.

C5 CONTINUOUS MEMORY DIAGNOSTIC TROUBLE CODE (DTC) 152 OR 151: CHECK SENSOR

Continuous Memory DTC 152 indicates that the sensor signal was greater than the self-test maximum. The DTC was generated under normal driving conditions.

Continuous Memory DTC 151 indicates that the sensor signal was less than the self-test minimum. The DTC was generated under normal driving conditions.

Sensors	Continuous Memory DTCs
IAT	152 and 151

Possible causes:

Worn or damaged sensor.
Open circuit in harness.
Grounded circuit in harness.
Worn or damaged PCM.

Enter Key On Engine Off Continuous Monitor Diagnostic Test Mode (DTM).
Turn on STAR tester beeper.

Tap on the sensor to simulate road shock.

Is a concern indicated?

Yes	No
DISCONNECT and inspect connectors. If OK, REPLACE the sensor. CLEAR Continuous Memory. RERUN Scan Tool Diagnostic Test.	GO to C6.

C6 CHECK EEC VEHICLE HARNESS

Still in Key On Engine Off Continuous Monitor DTM.
Observe for fault indication while performing the following:

Grasp the vehicle harness close to the sensor connector. Wiggle, shake or bend a small section of the closed loop system vehicle harness while working your way to the dash panel. Also wiggle, shake or bend the closed loop system vehicle harness from the dash panel to the PCM.

Is a concern indicated?

Yes	No
ISOLATE concern and SERVICE as necessary. CLEAR Continuous Memory. RERUN Scan Tool Diagnostic Test.	GO to C7.

C7 CHECK PCM AND VEHICLE HARNESS CONNECTORS

Key off.
Disconnect powertrain control module (PCM). Disconnect sensor connector. Inspect for damage, loose or pushed-out pins, loose or poorly crimped wires.

Are connectors and terminals OK?

Yes	No
Unable to duplicate and/or identify concern at this time. RERUN Scan Tool Diagnostic Test.	SERVICE as necessary. CLEAR Continuous Memory. RERUN Scan Tool Diagnostic Test.