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 ACT and VAT sensors. 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. For test results to be valid, avoid performing test in unusually hot or cold conditions.
This circuit test is intended to diagnose the following components and circuits:
- ACT Sensor
- ECT Sensor
- Vehicle Harness Circuits (ACT, ECT & SIG RTN)
- ECA
| Pin No. | Ckt. No. | (Ckt. Title) | Wire Color |
|---|---|---|---|
| Pin 7 | 354 | (ECT) | Light Green/Red |
| Pin 25 | 357 | (ACT) | Light Green/Purple |
| Pin 40 | 60 | (PWR GND) | Black/Light Green |
| Pin 46 | 359 | (SIG RTN) | Gray/Red |
| Pin 60 | 60 | (PWR GND) | Black/Light Green |
| Pin No. | Ckt. No. | (Ckt. Title) | Wire Color |
|---|---|---|---|
| Pin 7 | 354 | (ECT) | Light Green/Red |
| Pin 25 | 743 | (ACT) | Gray |
| Pin 40 | 570 | (PWR GND) | Black/Light Green |
| Pin 46 | 359 | (SIG RTN) | Gray/Red |
| Pin 60 | 570 | (PWR GND) | Black/Light Green |
To prevent replacing good components, ensure the following non-EEC areas or components are not the cause of problem:
- Coolant Level Low
- Electro Drive Cooling Fan
- Engine Oil Level Low
- Thermostat
- Air Cleaner Duct
- Cooling System, Water Pump or Fan
- Engine Operating Temperature Low
- Heat Riser Duct Valve
- Ambient Temperature Too Low
1) Code 21/116 Or 24/114: Check Installation & Operation Of Temperature Sensor Codes 21/116 (ECT) or 24/114 (ACT) indicates that the corresponding sensor is out of self-test range. Correct range for measurement is .3-3.7 volts. Check for the following possible causes:
- Low Ambient Temperature (Less Than 50°F)
- Low Coolant Level
- Faulty Harness Connector
- Faulty Sensor
- ACT sensor improperly mounted in air cleaner
If vehicle cannot be started, go to step 3). If vehicle stalls, or starts then dies, go to TEST S, step 1).
3) Check Temperature Sensor Resistance With Engine Off Turn ignition off and wait 10 seconds. Disconnect suspected sensor. Set DVOM on 200-k/ohm scale. Measure resistance between sensor signal circuit and SIG RTN circuit at sensor. See ACT & ECT SENSOR SPECIFICATIONS table below for voltage/resistance specifications.
| Temperature In °F (°C) | Voltage | Reading In Ohms |
|---|---|---|
| 50 (10) | 3.5 | 58,750 |
| 68 (20) | 3.1 | 37,300 |
| 86 (30) | 2.6 | 24,270 |
| 104 (40) | 2.1 | 16,150 |
| 122 (50) | 1.7 | 10,970 |
| 140 (60) | 1.3 | 7,700 |
| 158 (70) | 1.0 | 5,370 |
| 176 (80) | .8 | 384 |
| 194 (90) | .6 | 280 |
| 212 (100) | .5 | 207 |
| 230 (110) | .4 | 155 |
If resistance is within specification, perform the following step as applicable.
- For ECT sensor with a no-start condition, go to TEST A, step 1). DO NOT service code 21/116 at this time.
- For all others, go to next step.
If resistance is not within specification, replace suspected sensor. Reconnect vehicle harness and rerun QUICK TEST.
4) Check Temperature Sensor Resistance With Engine Running If engine has cooled down, warm engine before measuring ECT sensor resistance. Check for an open thermostat. Turn ignition off and wait 10 seconds. Disconnect suspected sensor. Run engine at 2000 RPM for 2 minutes. Set DVOM on 200-k/ohm scale. Measure resistance between sensor signal circuit and SIG RTN circuit at temperature sensor. See the ACT & ECT SENSOR SPECIFICATIONS table in this test for voltage/ resistance specifications. If resistance is within specification, replace ECA; reconnect components and repeat QUICK TEST. If sensor is not within specification, replace ECT sensor. Reconnect components and repeat QUICK TEST.
10) Code 51/118 Or 54/113: Induce Opposite Code (61/117 Or 64/112) Code 51/118 (ECT) or 54/113 (ACT) and 58 (VAT) indicate that the corresponding sensor signal is greater than the self-test maximum. Maximum signal voltage for ECT and ACT sensors is 4.6 volts. Maximum signal voltage for VAT sensors is 3.5 volts. Possible causes for excess voltage signals are as follows:
- Open circuit in vehicle harness (ACT or ECT)
- Faulty connection
- Faulty sensor
- Faulty ECA
Turn ignition off and wait 10 seconds. Disconnect suspected temperature sensor. Connect a jumper wire between sensor signal circuit and SIG RTN circuit at temperature sensor vehicle harness connector. Perform KOEO SELF-TEST. See KEY ON ENGINE OF (KOEO) SELF-TEST under QUICK TEST. If Code 61, 64, 112 or 117 is displayed, replace suspected sensor. Remove jumper wire, reconnect vehicle harness 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 and wait 10 seconds. Ensure suspected temperature sensor is disconnected. Disconnect ECA 60-pin connector. Check for damaged wiring and repair as necessary. Install breakout box, leaving ECA disconnected. Set DVOM on 200-ohm scale. Measure resistance between test pin No. 7 (ECT sensor) or test pin No. 25 (ACT sensor) at breakout box and sensor signal circuit at sensor vehicle harness connector. Also measure resistance between test pin No. 46 and SIG RTN circuit at sensor vehicle harness connector. If both readings are less than 5 ohms, replace ECA. Remove breakout box, reconnect components and rerun QUICK TEST. If either reading is 5 ohms or more, repair open circuits. Remove breakout box, reconnect components and rerun QUICK TEST.
20) Code 61/117 or 64/112: Induce Opposite Code (51/118 or 54/113) Code 61/117 (ECT) or 64/112 (ACT) indicates that sensor signal is less than the self-test minimum. Minimum signal for ACT and ECT sensor is 0.2 volt. Minimum signal for VAT sensor is 0.35 volt. Possible causes for this fault are as follows:
- Circuit grounded in vehicle harness (ACT or ECT)
- Faulty sensor
- Faulty ECA
- Faulty connection
Turn ignition off and wait 10 seconds. Disconnect vehicle harness connector from suspected 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 code 51, 54, 113 or 118 is not displayed, go to next step.
21) Check VREF Circuit Voltage at TPS Turn ignition off and wait 10 seconds. Set DVOM on 20-volt scale. Disconnect TPS. With ignition on and engine off, measure voltage between VREF and SIG RTN at TPS vehicle harness connector. If reading is less than 4 volts or more than 6 volts, go to TEST C, step 1). If reading is 4-6 volts, connect TPS and go to next step.
22) Check Temperature Sensor Signal For Shorts to Ground Turn ignition off and wait 10 seconds. Disconnect suspected sensor. Disconnect ECA 60-pin connector. Check for damaged wiring and repair as necessary. Install breakout box, leaving ECA disconnected. Set DVOM on 200-k/ohm scale. Measure resistance between test pin No. 7 (ECT) or test pin No. 25 (ACT) and test pins No. 40, 46, and 60. If any reading is less than 10 k/ohms, repair short circuit. Remove breakout box, reconnect components and repeat QUICK TEST. If all readings are 10 k/ohms or more, replace ECA. Remove breakout box and reconnect components. Repeat QUICK TEST.
90) Continuous Memory Code 51/118, 54/113, 61/117 or 68/112: Check Sensor A Continuous Memory Code 51/118 and 54/113 indicates that sensor signal is greater than the self-test maximum of 4.6 volts. The code is set during normal driving conditions.
Continuous Memory Code 61/117 and 64/112 indicates that sensor signal is less than the self-test minimum of 0.2 volt. The code is set during normal driving conditions.
Possible causes for these faults are as follows:
- Faulty sensor
- Faulty ECA
- Open or grounded circuit in harness
| Sensor | Continuous Memory Code |
|---|---|
| ACT | 54/113, 64/112 |
| ECT | 51/118, 61/117 |
Enter KOEO wiggle test mode. See CONTINUOUS MONITOR MODE (WIGGLE TEST) under QUICK TEST. Observe VOM or diagnostic 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 next step.
91) Check EEC-IV Vehicle Harness While in CONTINUOUS MONITOR MODE (WIGGLE TEST), observe VOM or diagnostic tester while wiggling and bending EEC-IV harness from sensor to cowl, a small section at a time. Also check harness from cowl to ECA. If fault is indicated, isolate fault and repair as necessary. Clear continuous memory and repeat QUICK TEST. If no fault is found, go to next step.
92) Inspecting ECA & Vehicle Harness Connectors Turn ignition off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect both connector and connector terminals for obvious 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, clear codes and repeat QUICK TEST. Refer to INTERMITTENTS in the TESTS W/O CODES article.