This code pops up about every other day. I read what it is, but what causes it and how do I fix it? Thanks

 

You might read this info:

http://www.gearchatter.com/viewtopic10367.php

Hope it helps

 

P0128 is a coolant temperature code, coolant no reaching operating temperature. Defective thermostat (stuck open), engine coolant temp sensor, coolant bypass problem.

 

Quite common with low thermos (160)-- On my Silverado i kept getting this code with a 160 thermo--I just set the enablers on P0128 to "not reported & no mill"---quit coming on--

 

Bad advice, I have a 160 degree thermostat in my current C5 and never saw this code, I also put one in my last C5 and never had the code show there either.

If you have a fault with your car and you want to "jerry-rig" your way around the problem thats fine, but please dont recommend those as permanent fixes.

 

only had the car for a month. just had a water pump put on the day before I bought it. any chance that has something to do with it?

 

Here are the theory of operation and diagnostic for this code. Check the things you can without a Tech 2 and see if you can find the problem.

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, P0116, 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 intake 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.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
Step 3. This step tests for excessive resistance in the ECT circuit.
Step 7. 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

Step 1 Did you perform the Diagnostic System Check-Engine Controls? -- Go to Step 2
Go to Diagnostic System Check - Engine Controls

Step 2 Is the cooling system low on coolant? -- Go to Loss of Coolant in Engine Cooling Go to Step 3

Step 3
1. Turn OFF the ignition.
2. Disconnect the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement .
3. Connect a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the ECT sensor.
4. Turn ON the ignition, with the engine OFF.
5. 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

Step 4
1. Turn OFF the ignition.
2. Disconnect the ECT sensor.
3. 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.
4. Turn ON the ignition, with the engine OFF.
5. 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

Step 5
1. Test the ECT sensor reference low circuit for a high resistance or an open.
2. 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
--

Step 6
1. Test the ECT sensor signal circuit for a high resistance or an open.
2. 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
--

Step 7
1. Remove the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement .
2. Suspend the ECT sensor and a thermometer in a pan of water.
3. Place the pan on a burner or hot plate.
4. 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

Step 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 --

Step 9 Replace the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement .
Did you complete the replacement? -- Go to Step 10
--

Step 10
1. Use a scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. 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 Diagnostic Aids

Step 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

Bill

 

I said IF he has a 160 thermo then this is a common code--The only fix would be to put the stock thermo (195) back in or live with the codes--or delete the p0128---If he does not have a 160 --then that would indicate some other reason for the engine not coming up to temperature--
With a 160 thermo--and no other problems-- there is no other way around fixing the code other than to delete it--You should read what i said before you critisize--

PS: It is more probable to set the code with non electric fanned engines as the fan is spinning at some speed all the time- with electric fans--the engine has an oppurtunity to come up to temperature before the fans kick on-Ther is NO table in the ECM where you can adjust the thermo temp--so it is always assumed by the ECM that you have a STOCK thermo in it when it comes to diagnostics--

 

[QUOTE=tblu92;1562960207]I said IF he has a 160 thermo then this is a common code--The only fix would be to put the stock thermo (195) back in or live with the codes--or delete the p0128---If he does not have a 160 --then that would indicate some other reason for the engine not coming up to temperature--
With a 160 thermo--and no other problems-- there is no other way around fixing the code other than to delete it.


totally agree.


With today’s modern sophisticated electronics, engine and transmission control modules are calibrated to work within a programmed operating coolant temperature range of about 180/195 degrees, to optimize performance of the vehicle, and most thermostats are calibrated within that range. By lowering the designed operating temperature, the coolant temperature sensor (set too thermostat range) will not command the engine control module into closed loop, Most of the vehicle emission
Controls, such as spark timing, fuel control, EGR operation with not function properly, affecting performance. Most importantly a vehicle operating in open loop mode, will run rich; that raw fuel dumped into the exhaust will cause expensive catalytic converter failure. If you what performance, don’t lower the designed operating temperature, tune your vehicle for it.

 

What He Said! ...........Hi Blu.

 

You guys can believe whatever you want, I'm just telling you that I am currently running a 160 degree thermostat in my 04 Coupe and am not getting any fault codes and I also had a 160 degree thermostat in my 03 convertible which didn't throw any fault codes.

 

I bought the car in Miami. Had no issues until It got cold here in Baltimore. Guess there no way to know what thermo is in it. Might have to just replace it with one I know is right.

 

That would be the first step.
Do you have any mods to the car?

Not to get in a pissing contest with others, but I also have a 160 thermo.
Have not ever experienced P0128. It maybe because of my fan settings.
Allowing my coolant to stay at or above 160. Supposedly my 160 fully
opens around 171+/-. So deleting the MIL
Anyway my point is with Frankiexx living in Maryland it is possible that you have a 160
and your fan settings are set way to low for being in the north versus the south.
That is of course if it has been changed.
You still have somethings to check, follow the DTC chart posted
by Bill Dearborn

 

What is the coolant temp? How long is the engine operating before you get the code?

 

I have no idea about mods. Bought it from a dealer in Miami. No documentation for anything, so I wouldnt have a clue. only thing obvious is a k&n air filter. This is my first vette, so I don`t know alot about them or how to work on them, thats why I`m here asking alot of questions some might think are trivial. Glad everyone has been so helpful. I`ll check the coolant temp next time it comes on. Usually comes on between 12 and 15 mins after I leave in the morning.

 

Watched temp on the way to work this morning. Outside temp was about 35. Coolant temp stayed between 133 and 140. 25 min drive at highway speeds. On the way home 47 outside, coolant temp never got above 144.

 

I would think you are having thermo stat related issues, for it to stay that
cool to never get above 144 either it is stuck open or you do not have
one.

 

On your next long drive turn the heater on, if it blows cold the thermostat is stuck open or missing, like not installed. Install the correct OEM thermostat and your engine well live longer and prosper. There is a REASON for a factory P0128 code.

Running with no thermostat or a lower number is old school, I been there, did that in the70s.not much benefit at all.

 

Ran the heater this morning. It blows decent heat. Won`t run you out, but it makes it comfortable in the car. Anyone know what thermo (temp) is correct? Would I be better off getting one from the stealership, or any one from an auto parts place? Thanks again. Frank

 

I am not trying too insulting you, take the car too a shop, let them diagnose the problem.


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