Circuit Test B5

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. Code 21 indicates that the ECT is out of the 0.3-3.5 volt Self-Test range. Possible causes for this fault are ECT resistance out of limits or a 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 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. Refer to wiring diagram in CIRCUIT TEST B8 . 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 SIGNAL RETURN. If voltage is less than 4 volts or more than 6 volts, go to CIRCUIT 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. Checking ECT Resistance: No Start Condition. With key off, disconnect ECT sensor and set DVOM on 200K-ohm scale. Measure resistance of ECT sensor. If resistance is within specifications, DO NOT  service Code 21 at this time. Go to CIRCUIT TEST A1 . If resistance is not within specification, replace ECT sensor.
5. Code 51: Generate Code 61. Code 51 indicates that the ECT signal was greater than the Self-Test maximum value of 4.6 volts (open circuit). Possible causes for this fault are a faulty ECT sensor, open circuit or faulty ECA. 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 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, remove jumper wire and go to next step.
6. 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.
7. Code 61: 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 of this fault are a faulty ECT, grounded circuit or faulty ECA. Turn key off and wait 10 seconds. Disconnect ECT sensor and inspect connector for damage or corrosion. Repair wiring and repeat 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 VREF at TPS. Refer to wiring diagram in CIRCUIT TEST B8 . 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 CIRCUIT TEST A3 , step 1). If voltage is between 4 and 6 volts, connect 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 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.
10. Continuous 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. 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. Clear codes and repeat QUICK TEST. If no fault is indicated, go to next step.
11. Checking 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 firewall. Also test harness from firewall to ECA in same manner. If fault is indicated, isolate fault in wiring and repair as necessary. Clear codes 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 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. Go to next step.
13. Continuous 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 of this fault 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 steps 10) and 11).