DTC Advanced Diagnostics: P0128 (3.0L Engine)
DTC P0128: Cooling System Malfunction
General Description
The abnormality of the thermostat is monitored by engine coolant temperature (ECT) sensor 1 and estimated engine coolant temperature. The estimated engine coolant temperature is calculated from the driving condition. If either of the following condition occurs, the powertrain control module (PCM) detects a malfunction and stores a DTC.
- Malfunction determination 1
The ECT sensor 1 value is less than a specified value when the estimated engine coolant temperature reaches a certain value.
- Malfunction determination 2
The estimated engine coolant temperature does not lower from a certain value, and the ECT sensor 1 value is less than a specified value.
Monitor Execution, Sequence, Duration, DTC Type
| Execution | Once per driving cycle*, Continuous** |
| Sequence | None |
| Duration | 10 seconds or more |
| DTC Type | Two drive cycles, MIL on |
*: Malfunction determination 1**: Malfunction determination 2
Enable Conditions
Malfunction determination 1
| Condition | Minimum | Maximum |
|---|---|---|
| Engine coolant temperature at engine start [ECT Sensor 1] | - | 115.5 deg.F (46.4 deg.C) |
| Intake air temperature [IAT Sensor (1)] | 14 deg.F (-10 deg.C) | - |
| Estimated engine coolant temperature | 171 deg.F (77 deg.C) | - |
| Idling ratio | - | 50 % |
[ ]: HDS Parameter
Malfunction determination 2
| Condition | Minimum | Maximum |
|---|---|---|
| Maximum engine coolant temperature before monitoring start | 150.5 deg.F (65.8 deg.C) | - |
| Intake air temperature [IAT Sensor (1)] | 14 deg.F (-10 deg.C) | - |
| Estimated engine coolant temperature | 167 deg.F (75 deg.C) | - |
| Idling ratio | - | 50 % |
Malfunction Threshold
- Malfunction determination 1:
The ECT sensor 1 value [ECT Sensor 1] is less than 150.5 deg.F (65.8 deg.C) when the estimated engine coolant temperature reaches 171 deg.F (77 deg.C).
- Malfunction determination 2:
The estimated engine coolant temperature does not lower from 167 deg.F (75 deg.C), and the ECT sensor 1 value [ECT Sensor 1] is less than 140 deg.F (60 deg.C).
Possible Cause
- Thermostat failure
- ECT sensor 1 failure
Confirmation Procedure
Operating Condition
- Start the engine under the following condition:
-
- ECT sensor 1 [ECT Sensor 1] at engine start is less than 115.7 deg.F (46.5 deg.C)
- Outside air temperature is more than 14 deg.F (-10 deg.C)
- Drive the vehicle at vehicle speed [Vehicle Speed] between 15 - 75 mph (24 - 120 km/h) for at least 30 minutes.
- Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow.
Diagnosis Details
Conditions for setting the DTC
When a malfunction is detected during the first drive cycle with the engine coolant temperature and intake air temperature at engine start-up within the specified temperature range, a Pending DTC is stored in the PCM memory. If the malfunction returns in the next (second) drive cycle with the engine coolant temperature and intake air temperature at engine start-up within the specified temperature range, the MIL comes on and a Confirmed DTC, the freeze data, and the on-board snapshot are stored.
Conditions for clearing the DTC
The MIL is cleared if the malfunction does not return in three consecutive trips in which the diagnostic runs. The MIL, the Pending DTC, the Confirmed DTC, the freeze data, and the on-board snapshot can be cleared with the scan tool clear command.