P2181
P2181-COOLING SYSTEM PERFORMANCE
Special Tools:
For a complete wiring diagram, refer to the Wiring Information.
Theory of Operation
The Powertrain Control Module (PCM) predicts what the engine coolant temperature should be, based on the engine coolant temperature at start-up, ambient temperature and how the vehicle is subsequently driven. The predicted engine coolant temperature is compared to the Engine Coolant Temperature Sensor reading. The error between the two is calculated and integrated with respect to time. When the Thermostat diagnostic runs, the integrated error is compared to a calibrated threshold and pass/fail is determined. Separate pass and fail thresholds are used in order to improve accuracy of the diagnostic.
- When Monitored:
Ignition on, Engine running and no ECT DTCs present.
- Set Condition:
Powertrain Control Module (PCM) recognizes that the ECT Sensor has failed its self coherence test. The coolant temp should only change at a certain rate, if this rate is too slow or too fast this fault will set. Two trip fault. Three good trips to clear MIL. The MIL and ETC light will illuminate.
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.
1. ACTIVE DTC
1. Ignition on, engine not running.
NOTE: If this code sets during extreme ambient temperatures, improper installation of a block heater may cause this DTC to set.
2. With the scan tool, select View DTCs.
3. Diagnose all other ECT and Cooling System codes before continuing.
Is the DTC Active at this time?
Yes
- Go To 2
No
- Perform the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition Test.
2. LOW COOLANT LEVEL
NOTE: If an Engine Coolant Temperature (ECT) DTC is set along with this code, diagnose the ECT DTC first.
NOTE: Inspect the ECT Sensor terminals and related PCM terminals. Make sure the terminals are free from corrosion and damage.
NOTE: The best way to diagnose this DTC is to allow the vehicle to sit overnight outside in order to cold soak the engine.
NOTE: Extreme cold ambient temperatures may cause this DTC to set.
NOTE: Inspect that there are no changes to the Cooling System that would make the warm up much slower or much faster: worn water pump, addition of aftermarket auxiliary cooler or a performance thermostat.
WARNING: Never open the cooling system when the engine is hot. The system is under pressure. Failure to follow these instructions can result in personal injury or death. Allow the engine to cool before opening the cooling system.
1. Inspect the coolant system for proper level and condition. Testing and Inspection
Is the coolant level and condition OK?
Yes
- Go To 3
No
- Inspect the vehicle for a coolant leak and add the necessary amount of coolant. [1][2]Specifications.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
3. THERMOSTAT
NOTE: This test works best if performed on a cold engine (cold soak).
1. Ignition on, engine not running.
2. With the scan tool, read the Eng Coolant Tmp Deg value. If the engine was allowed to sit overnight (cold soak), the temperature value should be a value that is close to the ambient temperature.
NOTE: If engine coolant temperature is above 82° C (180° F), allow the engine to cool until 65° C (150° F) is reached.
3. Start the Engine.
4. During engine warm-up monitor the Eng Coolant Tmp Deg value. The temp deg value change should be a smooth transition from start up to normal operating temp 82° C (180° F). Also monitor the actual coolant temperature with a thermometer.
NOTE: As the engine warms up to operating temperature, the actual coolant temperature (thermometer reading) and the Eng Coolant Tmp Deg on the scan tool should stay relatively close to each other.
5. Using the appropriate Service Information, determine the proper opening temperature of the thermostat. Engine Coolant Thermostat - Description
Did the thermostat open at the proper temperature?
Yes
- Go To 4
No
- Replace the thermostat.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
4. ECT SENSOR
1. Turn the ignition off.
2. Disconnect the ECT Sensor harness connector.
3. With the scan tool, read the ECT voltage.
4. Connect a jumper between the (K2) ECT Signal circuit and the (K900) Sensor ground circuit in the ECT Sensor harness connector.
Is the voltage below 1.0 Volt with the jumper wired installed?
Yes
- Verify that there is good pin to terminal contact in the ECT Sensor and Powertrain Control Module connectors. If OK, replace the ECT Sensor. Engine Coolant Temperature Sensor - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 5
5. (K2) ECT SIGNAL CIRCUIT SHORTED TO VOLTAGE
1. Turn the ignition off.
2. Disconnect the C2 PCM harness connector.
3. Ignition on, engine not running.
4. Measure the voltage on the (K2) ECT Signal circuit in the ECT Sensor harness connector.
Is there any voltage present?
Yes
- Repair the short to voltage in the (K2) ECT Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 6
6. (K2) ECT SIGNAL CIRCUIT OPEN
1. Turn the ignition off.
CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install the PCM Pinout Box to perform diagnosis.
2. Measure the resistance of the (K2) ECT Signal circuit from the ECT Sensor harness connector to the appropriate terminal of PCM Pinout Box.
Is the resistance below 5.0 Ohms?
Yes
- Go To 7
No
- Repair the open or excessive resistance in the (K2) ECT Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
7. (K900) SENSOR GROUND CIRCUIT OPEN
1. Measure the resistance of the (K900) Sensor ground circuit from the ECT Sensor harness connector to the appropriate terminal of PCM Pinout Box.
Is the resistance below 5.0 Ohms?
Yes
- Go To 8
No
- Repair the open or excessive resistance in the (K900) Sensor ground circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
8. (K2) ECT SIGNAL CIRCUIT SHORTED TO GROUND
1. Measure the resistance between ground and the (K2) ECT Signal circuit in the ECT Sensor harness connector.
Is the resistance below 100 Ohms?
Yes
- Repair the short to ground in the (K2) ECT Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 9
9. (K2) ECT SIGNAL CIRCUIT SHORTED TO THE (K900) SENSOR GROUND CIRCUIT
1. Measure the resistance between the (K2) ECT Signal circuit and the (K900) Sensor ground circuit in the ECT Sensor harness connector.
Is the resistance below 5.0 Ohms?
Yes
- Repair the short between the (K900) Sensor ground and the (K2) ECT Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 10
10. POWERTRAIN CONTROL MODULE (PCM)
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the ECT Sensor and the Powertrain Control Module (PCM).
2. Look for any chafed, pierced, pinched or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the ECT Sensor and Powertrain Control Module connectors.
4. Perform any Technical Service Bulletins (TSBs) that may apply.
Were there any problems found?
Yes
- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Replace and program the Powertrain Control Module. Powertrain Control Module - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.