Two Wire Temp Sensor Diagnostic Testing

COMPLETE CIRCUIT DIAGNOSTICS USING THE ELECTRICAL TEST LEAD KIT: 

1. Check the ECU signal and sensor ground circuits together to determine if the temp sensor is faulty. Connect the (special tool #2064100081, Kit, Electrical Test Lead) to the temp signal and sensor ground circuits at the temp sensor harness connector. Move the switch on the Electrical Test Lead Kit between the open and closed positions while monitoring the scan tool. If monitoring for faults, the circuit high fault should set when switched to the open position and the circuit low fault should set when switched to the closed position. If the sensor voltage is available on the scan tool, monitor the voltage readings. The voltage should be 5.0 volts when switched to the open position and 0.0 volts when switched to the closed position. Move the switch to adjust and use the tool to vary the resistance while monitoring the ECU signal voltage on the scan tool. Pick the result from a, b, or c below that best matches the results. 
   1. If the faults set as described and the signal voltage is 5.0 volts and 0.0 volts  - the ECU and temp sensor circuits are testing good. The temp sensor is most likely faulty or has a poor connection at the harness connector. Check the temp sensor harness connector for pushed out, spread, corroded or dirty terminals before condemning the sensor. The internal resistance of the sensor can be measured and compared to the table (if available) to verify a faulty sensor.
   2. If the signal voltage is stuck low or only the circuit low fault sets  - the most likely cause is the temp sensor signal circuit shorted to chassis ground or the temp sensor ground circuit. Check the temp sensor signal circuit for a short to ground, or to the temp sensor ground circuit. If the signal circuit is not shorted, use the wiring information to check all related harness connectors in the system for pushed out, spread, corroded or dirty terminals before condemning an ECU. If no issues are found, the ECU is most likely faulty.
   3. If the signal voltage is stuck high or only the circuit high fault sets  - the most likely cause is an open or very high resistance in the temp sensor signal or temp sensor ground circuit. Continue testing in step d.
   4. If the signal reading on the scan tool shows voltage present when switched to closed  - remove the test lead from the sensor ground circuit and connect it to a good chassis ground while observing the voltage on the scan tool. If the voltage drops to 0.0 volts the resistance is in the temp sensor ground circuit. If the voltage is still present the resistance is in the temp sensor signal circuit. Check the appropriate circuit for high resistance. Typically, it should be less than 3.0 Ohms. If the circuits check good, continue testing in step e.
   5. If the circuits are checked and do not have excessive resistance  - use the wiring information to check all related harness connectors for pushed out, spread, corroded or dirty terminals before condemning the ECU. If no issues are found, replace the ECU in accordance with the service information.

COMPLETE CIRCUIT DIAGNOSTICS USING CONVENTIONAL VOLTAGE TESTING WITH A DVOM: 

1. Verify the temp sensor and ECU harness connectors are connected and locked properly.
2. Turn the ignition on. Back probe and measure the voltage on the temp sensor signal circuit at the Fuel Pump harness connector. Pick the result below that best matches the voltage reading.
   1. If the signal voltage is reading between 0.1 and 4.9 volts  - the temp sensor signal is most likely giving a legitimate reading. If the circuit fault is active and the voltage reading on the scan tool does not match the DVOM voltage reading, the ECU is likely faulty.
   2. If the signal measures a constant 0.0 volts  - this indicates that the temp sensor signal circuit is shorted to ground or has an open between the ECU and temp sensor. If the circuit high fault is set, the most likely failure is an open in the temp sensor signal circuit. If the circuit low fault is set, the most likely failure is a short to ground in the temp sensor signal circuit or possibly a faulty sensor (disconnecting the temp sensor harness connector and checking for the circuit high fault to become active would indicate that the temp sensor is most likely faulty). Continue testing in step 3.
   3. If the signal reading has a constant voltage above 6.0 volts  - this would indicate that the signal circuit is shorted to another voltage supply.
   4. If the signal reading has a constant 5.0 volts  - this indicates an open further downstream in the circuitry. Most likely the temp sensor or the temp sensor ground circuit. Continue testing in step 4.
3. Disconnect the temp sensor and ECU harness connectors and check the temp sensor signal circuit for high resistance and short to ground. If the signal circuit checks good, check all connectors in the system for pushed out, spread, corroded or dirty terminals before condemning a ECU. If all of the connectors check good, replace the ECU in accordance with the service information.
4. To check the temp sensor, move the test lead over and back probe the temp sensor ground circuit at the temp sensor harness connector.

TYPICAL TEMP SENSOR CIRCUIT LOW DIAGNOSTICS: 

1. To quickly eliminate the temp sensor as a possible cause with and active circuit low fault, disconnect the temp sensor harness connector while monitoring for the circuit high fault to become active on the scan tool.
   1. If the circuit high fault becomes active when the sensor is disconnected, the temp sensor is most likely faulty.
   2. If the circuit high fault does not become active, continue testing in step 2.
2. Disconnect the Power Inverter Module (PIM) harness connector to isolate the circuit. Check the temp signal circuit for continuity to both chassis ground and the sensor ground circuit.
   1. If there is continuity to either, repair the signal circuit for a short to ground or the sensor ground circuit.
   2. If the signal circuit is not shorted, replace the Power Inverter Module (PIM) in accordance with the service information.

TYPICAL TEMP SENSOR CIRCUIT HIGH DIAGNOSTICS: 

1. Disconnect the temp sensor harness connector and measure the temp sensor signal circuit voltage with the ignition on. The signal circuit voltage should be between 4.9 and 5.6 volts. If battery voltage is present, repair the sensor signal circuit for a short to another voltage supply circuit.
2. With an active fault, monitor the scan tool and connect a jumper across the terminals with the ignition on. Typically, the temp sensor signal voltage should change to 0 volts on the scan tool with the jumper in place. If the voltage data read is not available, check for the circuit low fault to set with the jumper in place. If either result occurs, the temp sensor is faulty.
   1. If either result occurs, the temp sensor is faulty.
   2. If the voltage does not change to 0 volts or the circuit low fault is not present with the jumper in place, continue testing in step 3.
3. Check the resistance of the temp sensor signal circuit and temp sensor ground circuit. Typically the circuit resistance should be less than 5.0 Ohms.
   1. If there is an open or high resistance in either circuit, repair the circuit.
   2. If the temp sensor signal and ground circuits test good, and the voltage is still reading high or only the circuit high fault is present, use the wiring information to check all related harness connectors for pushed out, spread, corroded or dirty terminals before condemning the Power Inverter Module (PIM). If no issues are found, replace the Power Inverter Module (PIM) in accordance with the service information.

TYPICAL TEMP SENSOR CIRCUIT PERFORMANCE/RATIONALITY DIAGNOSTICS: 

1. Disconnect the temp sensor harness connector and connect the Electrical Test Kit leads to the temp sensor harness connector.
2. Move the switch on the tool to open. The signal should read 5.0 volts and a circuit high DTC should be active or pending.
3. Next flip the switch to the closed position. The signal should read 0 volts and a circuit low fault should be active or pending. If the scan tool reads as described in steps 2 and 3, it would indicate the wiring and PIM are good and the sensor is likely faulty. If there is voltage present between 0 and 5.0 volts with the test tool in the closed position it would indicate there is likely resistance in one of the circuits. Continue to step a.
   1. To determine which circuit has resistance, remove the test lead connected to the temp sensor ground circuit and connect it to a good chassis ground.
      • If the signal changes to 0 volts it would indicate the temp sensor ground has resistance. Continue to step b.
      • If there is still voltage present it would indicate the temp sensor signal has resistance. Continue to step b.
   2. Confirm the suspect circuit issue by isolating the circuit and measuring the resistance of the circuit. If no resistance is measured, carefully check all connectors in the path of the circuit for spread or dirty/corroded terminals. If the circuits check good (no resistance), verify whether the issue is with the temp sensor or Power Inverter Module (PIM). Continue to step 4 or 5.
4. If a temp table is available, the sensor and Power Inverter Module (PIM) can be verified in one of the following ways.
   1. Move the switch to adjust and connect an Ohmmeter to the test leads and dial the tool to a resistance value in the table. Connect both leads to the temp sensor harness connector with the ignition on and monitor the data in the scan tool for the proper reading. Use the tool to vary the resistance while monitoring the temp sensor signal temperature/voltage on the scan tool. If the reading matches the table, the temp sensor is likely faulty.
   2. If the temp sensor actual temperature can be acquired or reasonably estimated, measure the resistance across the terminals of the temp sensor and compare to the value in the table. If the resistance of the sensor is not in range of the table, the temp sensor is likely faulty.
5. If a temp table is not available for the sensor being tested, connect the Electrical Test Kit leads to the harness connector and flip the switch to adjust. With the ignition on, monitor the scan tool data and slowly adjust the resistance in the circuit. The temperature/voltage value should change with the resistance change. If the value changes as the resistance is varied it would indicate that the temp sensor is likely faulty.

HOW TO VERIFY A Power Inverter Module (PIM) FAILURE:  A PIM that is faulty and not able to properly read the signal can usually be determined when opening and shorting the circuits and monitoring the signal voltage and fault codes. If the expected voltage reads or DTCs do not occur when opening and jumping the connector, and the circuits are not shorted or open, it would indicate a faulty PIM. Before condemning and PIM, always carefully check all connectors in the path of the circuit for water intrusion, spread, pushed out, burnt or corroded terminals.