Circuit Description
An engine coolant temperature (ECT) sensor monitors the coolant temperature.
This input is used by the powertrain control module (PCM) for engine control,
and as an enabling criteria for some diagnostics.
The air flow coming into the engine is accumulated and is used in order
to determine if the engine has been driven within the conditions that would
allow the engine coolant to heat up normally to the thermostat regulating
temperature. If the coolant does not increase normally, or if the coolant
does not reach the regulating temperature of the thermostat, diagnostics
that use the engine coolant temperature as an enabling criteria may not
run when expected.
This DTC will only run once per ignition cycle within enabling conditions.
This DTC will set when there has been an excessive amount of time to
reach the minimum coolant temperature required for closed loop fuel control.
Diagnostic Aids
DTC P0128 is designed to detect a skewed ECT sensor or a faulty
thermostat.
Excessive coolant flow through the bypass hose to the throttle body
may cause this DTC to set.
A skewed ECT sensor can cause a DTC P0128 to set.
A skewed IAT sensor can cause this DTC to set. The AIT sensor should
read near the ambient temperature, with the engine running.
Step
| Action
| Values
| Yes
| No
|
Schematic Reference:
Engine Controls Schematics
|
1
| Did you perform the Diagnostic System Check-Engine
Controls?
| --
| Go to
Step 2
| Go to
Diagnostic System Check - Engine Controls
|
2
| Is the cooling system
low on coolant?
| --
| Go to
Loss of Coolant
in Engine Cooling
| Go to
Step 3
|
3
|
- Turn OFF the ignition.
- Disconnect the ECT sensor.
Engine Coolant Temperature (ECT) Sensor Replacement
.
- Connect a 3-amp fused jumper wire between the signal circuit and
the low reference circuit of the ECT sensor.
- Turn ON the ignition, with the engine OFF.
- With a scan tool, observe the ECT sensor temperature.
Does scan tool indicate that the ECT sensor temperature is more than
the specified value?
| 138°C (280°F)
| Go to
Step 7
| Go to
Step 4
|
4
|
- Turn OFF the ignition.
- Disconnect the ECT sensor.
- Connect a 3-amp fused jumper wire between the signal circuit of
the ECT sensor and a known good ground. Refer to
Using Fused Jumper Wires
in Wiring Systems.
- Turn ON the ignition, with the engine OFF.
- With a scan tool, observe the ECT temperature.
Does the scan tool indicate that the ECT sensor temperature is more
than the specified value?
| 138°C 280°F)
| Go to
Step 5
| Go to
Step 6
|
5
|
- Test the ECT sensor reference low circuit for a high resistance,
or for an open.
- Repair the circuit as necessary. Refer to
Circuit Testing
and
Wiring Repairs
in Wiring Systems.
Did you find and correct the condition?
| --
| Go to
Step 10
| --
|
6
|
- Test the ECT sensor signal circuit for a high resistance or for
an open.
- Repair the circuit as necessary. Refer to
Circuit Testing
and
Wiring Repairs
in Wiring Systems.
Did you find and correct the condition?
| --
| Go to
Step 10
| --
|
7
|
- Remove the ECT sensor.
- Suspend the ECT sensor and a thermometer in a pan of water.
- Place the pan on a burner or on a hot plate.
- Test the resistance of the ECT sensor through the specified range
of temperatures.
Does the resistance and temperature closely match the Temperature vs
Resistance Table?
| 10°C (50°F)-90°C (194°F)
| Go to
Step 8
| Go to
Step 9
|
8
| Reinstall the ECT sensor. Refer
to
Engine Coolant Temperature (ECT) Sensor Replacement
.
Is the action complete?
| --
| Go to
Engine Fails To Reach Normal Operating Temperature
in Engine Cooling
| --
|
9
| Replace the ECT sensor. Refer
to
Engine Coolant Temperature (ECT) Sensor Replacement
.
Did you complete the replacement?
| --
| Go to
Step 10
| --
|
10
|
- Use the scan tool in order to clear the DTCs.
- Turn OFF the ignition for 30 seconds.
- Start the engine.
- Operate the vehicle within the Conditions for Running the DTC
as specified in the supporting text
Does the DTC run and pass?
| --
| Go to
Step 11
| Go to
Step 2
|
11
| With a scan tool, observe the stored information, Capture Info.
Does the scan tool display any DTCs that you have not diagnosed?
| --
| Go to
Diagnostic Trouble Code (DTC) List
| System OK
|
