Diagnostic Aids

Perform this test only when directed by QUICK TEST. Ambient air temperature must be at least 50°F (10°C) to receive valid input from IAT sensor. Engine coolant temperature must be greater than 50°F (10°C) to pass KOEO SELF-TEST and greater than 180°F (82°C) to pass KOER SELF-TEST. Voltage values in this test are based on a 5-volt VREF signal. Values may vary up to 15% due to sensor and VREF variations.

This circuit test is intended to diagnose the following components and circuits:

Intake Air Temperature (IAT) sensor.
Engine Coolant Temperature (ECT) sensor.
Wiring harness circuits (IAT, ECT and SIG RTN).
Powertrain Control Module (PCM).

To prevent replacing good components, ensure the following non-EEC areas or components are not cause of problem:

Coolant level low.
Cooling system, water pump or fan.
Engine operating temperature.
Engine oil level low.
Thermostat.
Air cleaner duct.
Ambient temperature.

Fig 1: Temperature Sensor Circuits & Connector Terminals

TEST PIN NO. 7 (ECT) WIRE COLOR I.D.

Application	Wire Color
2.0L	Yellow/Black

TEST PIN NO. 25 (IAT) WIRE COLOR I.D.

Application	Wire Color
2.0L	White/Light Green

TEST PIN NO. 46 (SIG RTN) WIRE COLOR I.D.

Application	Wire Color
2.0L	Black/Blue

1) Code 21/116 Or 24/114: Code 21/116 (ECT) or 24/114 (IAT) indicates corresponding sensor is out of self-test range. Correct range for measurement is .3-3.7 volts. Check for following possible causes:

Low ambient temperature (less than 50°F).
Low coolant level.
Faulty harness connector.
Faulty sensor.

If vehicle cannot be started, go to step 3). If vehicle stalls, go to CIRCUIT TEST S. Ensure upper radiator hose is hot and pressurized. Repeat QUICK TEST. If Code 21, 24, 114 or 116 is present, go to step 2). If none of these codes are present, service other codes as necessary.

2) Check VREF Circuit Voltage At TPS Turn ignition off. Disconnect Throttle Position Sensor (TPS). With ignition on and engine off, measure voltage at TPS wiring harness connector between VREF and SIG RTN. See Fig 2 . If voltage is 4-6 volts, reconnect TPS and go to step 3). If voltage is not 4-6 volts, go to CIRCUIT TEST C.

3) Check Temperature Sensor Resistance (KOEO) Turn ignition off. Disconnect suspect sensor. Measure resistance between SIG RTN terminal at sensor and SIG RTN terminal at sensor wiring harness connector. If resistance is not within specification, replace suspected sensor and repeat QUICK TEST. If resistance is within specification, perform following step as applicable.

For diagnosing vehicles with ECT sensor and a no-start condition, DO NOT service Code 21/116 at this time. Go to CIRCUIT TEST AA for models equipped with distributor.
For other vehicles, go to step 4).

Fig 2: Identifying TPS Harness Connector Terminals

4) Check Temperature Sensor Resistance (KOER) Warm engine to normal operating temperature. Turn ignition off. Disconnect suspect sensor. Run engine at 2000 RPM for 2 minutes. Measure resistance between SIG RTN terminal at sensor and SIG RTN terminal at sensor wiring harness connector. See ACT & ECT SENSOR SPECIFICATIONS table. If resistance is within specification, replace PCM and repeat QUICK TEST. If sensor is not within specification, replace sensor and repeat QUICK TEST.

ACT & ECT SENSOR SPECIFICATIONS

Temperature °F (°C)

⁽¹⁾ Volts

⁽¹⁾ Ohms

50 (10)

3.51

58,750

68 (20)

3.07

27,300

86 (30)

2.60

24,270

104 (40)

2.13

16,150

122 (50)

1.70

10,970

140 (60)

1.33

7700

158 (70)

1.33

7700

176 (80)

0.78

3840

194 (90)

0.60

2800

212 (100)

0.46

2070

⁽¹⁾	Values may vary by 15 percent.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 4) to step 10). No test procedures have been omitted.

10) Code 51/118 Or 54/113: Induce Opposite Code (Code 61/117 Or 64/112) Code 51/118 (ECT) or 54/113 (IAT) indicate corresponding sensor signal is greater than self-test maximum. Maximum signal voltage for ECT and IAT sensor is 4.6 volts. Possible causes for excess voltage signals are:

Open circuit in wiring harness (IAT or ECT).
Faulty connection.
Faulty sensor.
Faulty PCM.

Turn ignition off. Disconnect suspect temperature sensor. Connect a jumper wire between SIG RTN terminal at sensor and SIG RTN terminal at sensor wiring harness connector. Repeat QUICK TEST. If Code 61, 64, 112 or 117 is displayed, replace suspect sensor and repeat QUICK TEST. If Code 61, 64, 112 or 117 is not displayed, remove jumper wire and go to next step.

11) Check Continuity Of Sensor Signal & SIG RTN Circuits Turn ignition off. Ensure suspect temperature sensor is disconnected. Disconnect PCM 60-pin connector. Check for damaged wiring, and repair as necessary. Install Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance of sensor signal circuit between test pin No. 7 (ECT sensor) or test pin No. 25 (IAT sensor) at breakout box and sensor signal circuit terminal at sensor wiring harness connector. Also measure resistance between test pin No. 46 and SIG RTN circuit at sensor wiring harness connector. If both readings are less than 5 ohms, replace PCM and repeat QUICK TEST. If either reading is 5 ohms or more, repair open circuit and repeat QUICK TEST.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 11) to step 20). No test procedures have been omitted.

20) Code 61/117 or 64/112: Induce Opposite Code (51/118 or 54/113) Code 61/117 (ECT) or 64/112 (IAT) indicates sensor signal is less than self-test minimum. Minimum signal for IAT and ECT sensor is 0.2 volt. Possible causes for this fault are:

Circuit grounded in wiring harness.
Faulty sensor.
Faulty PCM.
Faulty connection.

Turn ignition off. Disconnect wiring harness connector from suspect sensor. Check for damaged wiring, and repair as necessary. Repeat KOEO SELF-TEST. If Code 51, 54, 113 or 118 is displayed, replace sensor and connect harness. Repeat QUICK TEST. If Codes 51, 54, 113 or 118 is not displayed, go to step 21).

21) Check VREF Circuit Voltage At TPS Turn ignition off. Disconnect wiring harness connector from suspect sensor. Disconnect TPS. Turn ignition on. Measure voltage between VREF and SIG RTN at TPS wiring harness connector. If voltage is not 4-6 volts, go to CIRCUIT TEST C. If voltage is 4-6 volts, connect TPS and go to step 22).

22) Check Temperature Sensor Signal For Shorts To Ground Turn ignition off. Disconnect suspect sensor. Disconnect PCM 60-pin connector. Check for damaged wiring, and repair as necessary. Install Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between test pin No. 7 (ECT) or 25 (IAT) and pins No. 40, 46 and 60. If any reading is less than 10,000 ohms, repair short circuit and repeat QUICK TEST. If all readings are 10,000 ohms or more, replace PCM and repeat QUICK TEST.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 22) to step 90). No test procedures have been omitted.

90) Continuous Memory Code 51/118, 54/113, 61/117 Or 64/112: Check Sensor A Continuous Memory Code 51/118 or 54/113 indicates sensor signal is greater than self-test maximum of 4.6 volts. Code is set during normal driving conditions. Continuous Memory Code 61/117 or 64/112 indicates sensor signal is less than self-test minimum of 0.2 volt. Code is set during normal driving conditions. Possible causes for these faults are:

Faulty sensor.
Open or grounded circuit in harness.
Faulty PCM.

SENSOR CODES

Sensor	Continuous Memory Code
IAT	54/113 Or 64/112
ECT	51/118 Or 61/117

Enter KOEO wiggle test mode. See CONTINUOUS MONITOR MODE (WIGGLE TEST) under QUICK TEST. Observe analog voltmeter or scan tester for indication of fault while tapping sensor lightly and wiggling sensor connector. If fault is indicated, disconnect and inspect connector and terminals. If connector and terminals are okay, replace sensor, clear continuous memory and repeat QUICK TEST. If fault is not indicated, go to step 91).

91) Check EEC-IV Wiring Harness While in CONTINUOUS MONITOR MODE (WIGGLE TEST), observe analog voltmeter or scan tester while wiggling and bending wiring harness, a small section at a time, from sensor to cowl. Also check harness from cowl to PCM. If fault is indicated, isolate fault and repair as necessary. Clear continuous memory, and repeat QUICK TEST. If no fault is found, go to step 92).

92) Inspect PCM & Wiring Harness Connectors Turn ignition off. Disconnect PCM 60-pin connector. Inspect both connector and connector terminals for damage. If connectors and terminals are damaged, repair as necessary and repeat QUICK TEST. If connectors and terminals are okay and fault cannot be duplicated at this time, see INTERMITTENTS in TESTS W/O CODES - EEC-IV article in this section.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 92) to step 100). No test procedures have been omitted.

100) Continuous Memory Code 338 A Continuous Memory Code 338 indicates cooling system has not reached normal operating temperature. Possible causes for this fault are:

Thermostat stuck open.
Coolant outlet gasket leak.
Water pump gasket leak.

Repair cooling system as necessary. Clear continuous memory, and repeat QUICK TEST.

101) Continuous Memory Code 339 A Continuous Memory Code 339 indicates cooling system has overheated. Possible causes for this fault are:

Coolant level low.
Thermostat stuck closed.
Coolant system clogged.
Water pump damaged or worn.
Radiator cap damaged or worn.
Cooling fan damaged or worn.

Repair cooling system as necessary. Clear continuous memory, and repeat QUICK TEST.