Test B5 - Engine Coolant Temperature (ECT) Sensor

Fig 1: Engine Coolant Temperature (ECT) Sensor Circuit

To prevent replacement of good components, be aware that the following non-EEC related areas may be at fault: coolant or oil level, blocked or obstructed airflow, engine not at normal operating temperature, or cooling fan.

1. Code 21: Check Engine Temperature  - Start engine and run at 2000 RPM for 2 minutes. Check that upper radiator hose is hot and pressurized. Repeat QUICK TEST  before continuing. If vehicle stalls, DO NOT  service code 21 at this time, go directly to DIAGNOSIS BY SYMPTOM TEST  . If code 21 is not displayed, service other codes as necessary (if displayed). If code 21 appears, go to next step.
2. Checking for VREF at TPS  - Turn key off. Wait 10 seconds. Disconnect TPS. Set DVOM on 20-volt scale. With KOEO measure voltage at TPS harness connector between VREF and signal return. If voltage is less than 4 volts or more than 6 volts, go to TEST A3  , step 1). If voltage is between 4 and 6 volts, reconnect TPS and go to next step.
3. ECT Sensor Resistance  - Ensure engine is fully warmed up for this step. Turn key off and wait 10 seconds. Disconnect wiring harness at ECT sensor. Set DVOM on 200K-ohm scale and measure resistance of ECT sensor. If reading is 1300-7700 ohms at engine coolant temperature of 140-240°F (60-116°C) with engine off and 1550-4550 ohms at 180-230°F (82-110°C) with engine running, replace ECA, connect ECT sensor and repeat QUICK TEST  . If readings are not correct for coolant temperature, replace ECT sensor, connect harness, and repeat QUICK TEST.
4. Code 51: Generate Code 61  - Turn key off and wait 10 seconds. Disconnect ECT sensor at wiring harness and inspect wiring for damage or corrosion. Connect a jumper wire between ECT signal and signal return terminals in sensor harness connector. Repeat KEY ON/ENGINE OFF (KOEO) SELF-TEST  . If code 61 is displayed, replace ECT sensor and remove jumper wire. Reconnect harness to ECT sensor and repeat QUICK TEST  . If code 61 is not displayed, go to next step.
5. ECT Signal and Return Continuity Check  - Turn key off and wait 10 seconds. With harness disconnected at ECT sensor and jumper removed from harness connector, disconnect ECA 60-pin connector. Inspect for and repair any damaged wiring. Install breakout box, leaving ECA disconnected. Set DVOM on 200-ohm scale. Measure resistance between ECT signal at ECT connector and Test Pin No. 7. Measure resistance between signal return at ECT connector and Test Pin No. 46. If both readings are less than 5 ohms, replace ECA. Remove breakout box and connect ECA and ECT sensor. Repeat QUICK TEST  . If either reading is 5 ohms or more, repair open circuits. Remove breakout box, and connect ECA and ECT sensor. Repeat QUICK TEST.
6. Code 61: Generate Code 51  - Turn key off and wait 10 seconds. Disconnect ECT sensor and inspect connector for damage or corrosion. Repair wiring and repeat KEY ON/ENGINE OFF (KOEO) SELF-TEST  . If code 51 is displayed, replace ECT sensor, connect sensor, and repeat QUICK TEST  . If code 51 is not displayed, go to next step.
7. Checking VREF at TPS  - Turn key off and wait 10 seconds. Set DVOM on 20-volt scale. Disconnect TPS. Turn key on, leaving engine off. Measure voltage between VREF and signal return at TPS connector. If reading is less than 4 volts or more than 6 volts, go to TEST A3  , step 1). If voltage is between 4 and 6 volts, connect TPS and go to next step.
8. Checking ECT Signal for Ground Short  - Turn key off and wait 10 seconds. Disconnect harness from ECT sensor. Disconnect ECA 60-pin connector. Inspect for and repair any damaged wiring. Install breakout box, leaving ECA disconnected. Set DVOM on 200K-ohm scale. Measure resistance between Test Pin No. 7 and Test Pins No. 40, 46, and 60. If any reading is less than 10K ohms, repair short circuits. Remove breakout box, connect ECA and ECT sensor, and repeat QUICK TEST  . If all readings are 10K ohms or more, replace ECA. Remove breakout box, connect ECA and ECT sensor. Repeat QUICK TEST.
9. Continuous Code 21: Test Drive  - Turn key off and wait 10 seconds. Disconnect all SELF-TEST equipment and prepare vehicle for test drive. While driving vehicle, attempt to copy driving style in which complaint was noticed. If problem occurs, try to maintain condition for one or more minutes. After road test, repeat KEY ON/ENGINE OFF (KOEO) SELF-TEST  . If code 21 is present in CONTINUOUS SELF-TEST, ensure thermostat is working properly. If thermostat functions properly, replace ECT sensor. Repeat QUICK TEST  . If code 21 is not displayed, fault cannot be duplicated at this time. Continuous code 21 testing is complete.
10. Continuous Code 51 or 61: Check ECT Sensor  - Using CONTINUOUS MONITOR (WIGGLE) TEST  , observe VOM or diagnostic tester for indication of fault while tapping ECT sensor and wiggling ECT connector. If fault is indicated, disconnect and inspect ECT connector and terminals. If connector and terminals are okay, replace ECT sensor and repeat QUICK TEST  . If no fault is indicated, go to next step.
11. Checking Harness  - While in CONTINUOUS MONITOR (WIGGLE) TEST, observe VOM or diagnostic tester for indication of fault as you bend, shake or wiggle EEC-IV harness. Start at sensor connector and work toward firewall. Also test harness from firewall to ECA in same manner. If fault is indicated, isolate fault in wiring and repair as necessary. Repeat the QUICK TEST  . If there is no fault indicated, go to next step.
12. Checking ECA and Harness Connectors  - Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect both connectors and terminals for obvious damage. If connectors and terminals are damaged, repair as necessary and repeat QUICK TEST  . If connectors and terminals are okay, fault cannot be duplicated at this time. Continuous code 51 or 61 testing is complete.