Check Engine Light with code P0128 (10 PCM) - I used to get this before the head/cam package installation, now it's back. Anyone know what it means?

 

I believe this is the same one that I used to get all the time...it's the code for your engine not getting warm enough. What type of stat do you have? Does your temp take a long while to get to normal readings? I replaced my customized stat with a 160 stat and the problem's gone. Hope this helps!!!

 

Yeah, it's a water temp thing. I brought my service manual in if you want the whole wording, but you either have a low temp thermostat or you took it out and the engine is looking for the water to get to a certain temp. When the air temp is at...whatever...the engine temp (water) should be ???? If it doesn't come up to that, then you get the code.

Do you know how to reset those codes on the vette??? Option (twice), Fuel (4 times)???

 

Thanks guys. Yeah, I have a 172 degree thermostat.

 

DTC P0128
Circuit Description
An engine coolant temperature (ECT) sensor monitors the temperature of the coolant. 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 used to determine if the engine has been driven within the conditions that would allow the engine coolant to heat normally to the thermostat regulating temperature. If the coolant temperature does not increase normally, or does not reach the regulating temperature of the thermostat, the diagnostics that use the engine coolant temperature as an enabling criteria may not run when expected.

If the engine coolant fails to reach a preset target temperature before a calculated air flow is accumulated, P0128 will set.

This DTC will only run once per ignition cycle within the enabling conditions.

Conditions for Running the DTC
DTCs P0100, P0101, P0103, P0110, P0111, P0112, P0113, P0117, P0118, P0125, P0500, P0501, P0502, P0503, P1114, or P1115 are not set.
The coolant temperature is -40°C (-40°F) or more.
The coolant temperature is less than 70°C (158°F).
The air temperature is -7°C (19°F) or more.
The engine running for more than 2 minutes and less than 22 minutes.
The vehicle speed is more than 8 km/h (5 mph) for more than 2.4 km (1.5 miles).
The mass air flow average reading is more than 23 g/s.
Conditions for Setting the DTC
The length of time for the engine coolant to reach a preset temperature has been exceeded.

Action Taken When the DTC Sets
The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.
Conditions for Clearing the MIL/DTC
The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.
Diagnostic Aids
DTC P0128 is designed to detect a faulty thermostat.

Excessive coolant flow through the bypass hose to the throttle body may cause this DTC to set.

A skewed ECT sensor may cause a DTC P0128 to set.

A skewed intake air temperature (IAT) sensor may cause this DTC to set. The IAT sensor should read near ambient temperature with the engine running.

Test Description
The numbers below refer to the step numbers on the diagnostic table.

This step tests for excessive resistance in the ECT circuit.

This step tests for a skewed sensor through the range of temperatures affecting this DTC.

Step
Action
Value(s)
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. Refer to 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.
Use a scan tool in order to observe the ECT sensor temperature.
Does the 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.
Use a scan tool in order to 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 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 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. Refer to Engine Coolant Temperature (ECT) Sensor Replacement .
Suspend the ECT sensor and a thermometer in a pan of water.
Place the pan on a burner or 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?
10-90°C (50-194°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 a 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


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Document ID # 706918