Test B5 - 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. Service Code 21: Check Engine Operating Temperature. Code 21 indicates that the ECT is out of the 0.3-3.5 volt Self-Test range. Possible causes are: ECT resistance out of limits or faulty ECA. If engine will not start, go to step 4). 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 to TEST D19 - SYSTEM CHECK  . If code 21 is not displayed, service other codes as necessary. If code 21 appears, go to next step.
2. Checking for VREF at TPS. Turn key off and wait 10 seconds. Disconnect TPS. Set DVOM on 20-volt scale. With KOEO measure voltage at TPS harness connector between VREF and SIG RTN. See Fig 1 . If voltage is not 4-6 volts, go to TEST A3 - REF  . VOLTAGE, step 1). If voltage is 4-6 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. See Fig 1 . Set DVOM on 200K-ohm scale and measure resistance of ECT sensor. If reading is 1300 ohms (240°F) to 7700 ohms (140°F) with engine off and 1550 ohms (230°F) to 4550 ohms (170°F) with engine running, replace ECA. Reconnect ECT sensor and repeat QUICK TEST. If readings are not as specified, replace ECT sensor, connect harness, and repeat QUICK TEST.
4. Checking ECT Sensor Resistance With A No Start Condition. With key off, disconnect ECT sensor and set DVOM on 200K-ohm scale. Measure resistance of ECT sensor and compare with above ECT SENSOR SPECIFICATIONS  table. If resistance is within specifications, DO NOT  service Code 21 at this time. Go to TEST A1 - NO START  . If resistance is not within specification, replace ECT sensor, connect ECT sensor and repeat quick test.
5. Service Code 51: Attempt To Generate Code 61. Code 51 indicates that the ECT signal is greater than the Self-Test maximum value of 4.6 volts (open circuit). Possible causes are: faulty ECT sensor, open circuit or faulty ECA. Turn key off and wait 10 seconds. Disconnect wiring harness from ECT sensor. Inspect and repair wiring as necessary. Connect a jumper wire between ECT SIGNAL and SIGNAL RETURN terminals of ECT harness connector. See Fig 1 . Perform KOEO SELF-TEST. If Code 61 is displayed, replace ECT sensor, remove jumper wire, reconnect ECT sensor and repeat QUICK TEST. If Code 61 is not displayed, remove jumper wire and go to next step.
6. ECT Signal and Signal Return Continuity Check. Turn key off and wait 10 seconds. Disconnect harness from ECT sensor. Disconnect ECA 60-pin connector. Inspect and repair any damaged wiring. Install breakout box, leaving ECA disconnected. Set DVOM on 200-ohm scale. Measure resistance between ECT SIGNAL at ECT harness connector and test pin No. 7 at breakout box. Measure resistance between SIGNAL RETURN at ECT harness connector and test pin No. 46 at breakout box. If both readings are less than 5 ohms, replace ECA, remove breakout box, reconnect components and repeat QUICK TEST. If either reading is not less than 5 ohms, repair open circuit(s). Remove breakout box, and connect ECA and ECT sensor. Repeat QUICK TEST.
7. Service Code 61: Attempt To Generate Code 51. Code 61 indicates that the ECT signal is less than the 0.2 volt Self-Test minimum value (grounded circuit). Possible causes are: faulty ECT, grounded circuit or faulty ECA. Turn key off and wait 10 seconds. Disconnect ECT sensor. Inspect and repair connector and/or wiring as necessary. Perform 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.
8. Checking For 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 harness connector. See Figure . If reading is not 4-6 volts, go to TEST A3 - REF  . VOLTAGE, step 1). If reading is 4-6 volts, reconnect TPS and go to next step.
9. Checking ECT Signal for Short to Ground. Turn key off and wait 10 seconds. Disconnect harness from ECT sensor. Disconnect ECA 60-pin connector. Inspect 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 at breakout box. 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 and repeat QUICK TEST.
10. Continuous Memory Code 51: Check ECT Sensor. Code 51 indicates that the ECT signal was greater than the Self-Test maximum voltage of 4.6 volts sometime during vehicle operation. Possible causes are: faulty ECT sensor, open harness or faulty ECA. Enter KOEO 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, clear continuous memory and repeat QUICK TEST. If no fault is indicated, go to next step.
11. Checking EEC-IV Harness. While in KOEO 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 dash panel. Also test harness from dash panel to ECA in same manner. If fault is indicated, isolate fault in wiring and repair as necessary. Clear continuous memory and repeat QUICK TEST. If fault is not 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 damage and repair as necessary. Repeat QUICK TEST. If connectors and terminals are okay, fault cannot be duplicated at this time. Go to next step.
13. Continuous Memory Code 61: Check ECT Sensor. Code 61 indicates that the ECT signal was less than the 0.2 volt Self-Test minimum value (grounded circuit) sometime during vehicle operation. Possible causes are: faulty ECT, grounded circuit or faulty ECA. Using KOEO 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, repeat step 11).