PO128 nightmare please help

I have a 2001 Chevy S10 Xtreme Pickup

The light came on and the code was PO128.

I took it to a shop and they replaced the thermostat- the light came back on.

I took it back they replaced the sensor - the light came back on

I took it back they replaced the thermostat again- the light came back on

coolant level is fine- fan isnt running excessively etc.

took it to another shop- they replaced the thermostat and sensor again bc everyone says nothing is wrong with the truck- yep you guessed it the light came on again... WTF!

someone suggested maybe it was the onboard computer? the truck is NOT over heating but I cant have the light on and be able to pass emissions to get my tag.

Im seriously at my wits end here anyone have a clue what it might be? its always the same code (had several different places check the code) :banghead:

well, i don't have an immediate solution, but i'll see what i can dig up.

just wanted to say hello. i'm on the other side of 285 in lawrenceville, ga.

welcome to the forums!

any other lights coming on? maybe a bad coolant level sensor can cause that code. whats the operating temp looking like? what kind of coolant are you running, and when was it last flushed/serviced? i wonder if a bad radiator cap (loss of pressure) could throw that code...

dunno if you saw this already, but here are some ideas:
http://www.obd-codes.com/p0128

well, i don't have an immediate solution, but i'll see what i can dig up.

just wanted to say hello. i'm on the other side of 285 in lawrenceville, ga.

welcome to the forums!

any other lights coming on? maybe a bad coolant level sensor can cause that code. whats the operating temp looking like? what kind of coolant are you running, and when was it last flushed/serviced? i wonder if a bad radiator cap (loss of pressure) could throw that code...

dunno if you saw this already, but here are some ideas:
http://www.obd-codes.com/p0128

hey man thanks for the welcome - any help would be greatly appreciated- we are about to go insane over this.

we had the radiator cap replaced the last time it was in the shop just to be sure it wasn't it.

There have been no other codes... nothing

The coolant sensor has now been replaced twice - the coolant I'll have to check but I think its dexcon or something, Ill check. Radiator flush has been years you think that could be causing it?

is there something that could be shorting out the thermostat? I hate to pay to replace the computer if that still isn't going to solve the problem.

Not sure if this would cause the code. But has you coolant pick up an electrical charge?


Did they check:

Verify proper intake air temperature (IAT) sensor operation

Your Right on target there laxman21.

Not sure if this would cause the code. But has you coolant pick up an electrical charge?


Did they check:

Verify proper intake air temperature (IAT) sensor operation

thanks that was the only thing from the OBT codes that we havent done but the 1st shop we took it to said my model/year truck didnt have an air intake sensor - does anyone know if a 2001 chevy s-10 xtreme pick up does in fact have one?

as for the coolant picking up an electrical charge what can I do to fix that? have the system flushed?

P0128

The coolant is taking too long to warm up, theres more emission during cold.
1) Both the ECU Temp sensor + thremostat has been replaced.
2) The electric coolant fan should be off during the cold start + warm up.
3) The ECU is doing it's job, there could be a reflash software for this problem.
4) How old are the plugs + 02 sensors?
5) Clear code, and try letting the engine warm up, befor taking off.
This will also buy time to charge your battery.

Driving your truck to soon, the air flow threw the grill, and radiator could be keeping the coolant cold for a longer period of time.

What engine and transmission is in the vehicle?

After the vehicle sits overnight, and before you start the engine, find out what your local ambient temperature is. Compare it to the ECT and the IAT readings. All 3 should be within a degree or two at the most of each other.

What engine and transmission is in the vehicle?

After the vehicle sits overnight, and before you start the engine, find out what your local ambient temperature is. Compare it to the ECT and the IAT readings. All 3 should be within a degree or two at the most of each other.

the truck is a 2.2L 4 cylinder automatic

how do I find out those temp readings?

also not sure if it makes a difference or not but someone had asked me to test the thermostat that was given to me when the parts were changed out the last time- and it DID open when dropped in boiling water and it DID close back when removed- so if the actual thermostats are fine and the sensor has also been replaced twice.... what could it be?

also as of yesterday I no longer have heat or defrost - it blows air just never gets warm and this did not start until yesterday

i took the radiator cap off and there is coolant in both the radiator and reserve tanks.

Just droping it in boling water is not a good test.
To test it you have to moniter your pan of water tempture.
When it reaches 195 stat should open.

If you have lost heat and engine running tempt is not up to 195 put another know good stat in it.

To test and check your engine tempt sensor reading to vcm and IAT tempt sensor reading to computer you will need toget it on a scanner and read them out on scanner reading.

you might have a blockage somewhere. a coolant flush prob wouldnt be a bad place to start. Or maybe the shop is putting in a thermostat with too low of a temp rating, ie a 180 degree t-stat.

you might have a blockage somewhere. a coolant flush prob wouldnt be a bad place to start. Or maybe the shop is putting in a thermostat with too low of a temp rating, ie a 180 degree t-stat.

thanks man- someone else said a coolant system flush might be the problem so were going to try that

we checked the t-stats that are in the vehicle and the one that the guy just took off- they are both 195

i sure hope the flush does it- bc im at my wits end with this

You have not told us what engine running tempt is.
If you have no heat and engine running tempt is not getting up to 195 as fast as it should put another good brand stat in it.

You have not told us what engine running tempt is.
If you have no heat and engine running tempt is not getting up to 195 as fast as it should put another good brand stat in it.

the engine IS running at 195- the temp gauge looks like this \.....|...../ and the temp once the truck is warmed up is riding at the | part which says 195 above it-


we plan on having the flush done as soon as I can get the time off work


if that is not it...ill scream!

Flushing out heater core may help on heater heat.
But on the code you need to get it on a engine capable scanner and see what engine tempt and intake air tempt sensor to computer is reading in computer.

thanks man- someone else said a coolant system flush might be the problem so were going to try that

we checked the t-stats that are in the vehicle and the one that the guy just took off- they are both 195

i sure hope the flush does it- bc im at my wits end with this

When you kept going back to the first shop.. did they actually charge you for every repair every time you went back?