Had a CEL which showed fault code P0128. I cleared the code and checked the coolant level and it was just below the "Min" mark. I added enough coolant/water 50/50 to raise it between Min/Max. The light has not come back on since.
Would this be what caused the light or is there another possible reason?
Thanks

 

P0128 indicates the system has seen an inconsistency with the engine temperature. 90% of the time it is due to a failed/sticking thermostat. The usual scenario is the engine temp comes up and then as you drive the temp falls below the thermostat temp of 88 deg. C. The ECM knows the temp should stay at 88 Deg or above, if it doesn't, it sets P0128.

Cheers,

 

I've got P0128 on my 08 S-Type also. However, diagnostic shows "coolant temperature sensor". Nothing about overheat. Can anyone clue me in on what's really happening?

 

I think my last post pretty well covered it, what do you think is missing??

The ECM knows you start a car, temp goes up at such and such a rate, and should stay up at about 90-95 deg C. If it sees engine temp do something other than that.........sets a code.

Cheers,

 

+1

Worth reading the codes PDF (in the FAQs) as it gives details.

 

I recently had this same code (P0128) activate on my '03 4.2L after having a crack in my coolant tank that caused a slow leak. I had the tank replaced and the leak has stopped but the P0128 code has reappeared. I think the leak must have caused damage to the thermostat (or it just died of old age). How difficult is it to replace the thermostat? Thanks.

 

Thanks, guys. For xjrguy, I read your earlier post and appreciate the good advice. However, the readout I got on P0128 was "coolant temperature sensor", not "coolant thermostat malfunction". That would seem to indicate that the sensor was at fault, not the thermostat. Everyone who has posted on P0128 seems to have seen the "coolant thermostat malfunction:. I can't figure out why my readout was different. Is my (borrowed) reader giving me a false readout? Any insight would be welcome. I'd not like to replace the thermostat and find that the code for "sensor" was still there and then have to try the sensor. Thanks again for any assistance.

 

most everyone on here with tech status either still does work for a dealership or did and is now a independant and for many years. Iam at 14+Years. Readers are generic, we however are specific. Replace the thermostat. This is a prime example of why I tell people to have someone work on your car that works on them everyday. not GM, Ford, Toyota, Benz Jag etc... they may be cheaper but they will replace the sensor, thermostat and water pump. maybe fans and all hoses too. But then hey theyre alot cheaper at $90/hour

 

All that code means is that the ECM saw a temperature pattern that shouldn't occur if everything is working properly. That could be because of a sensor fault/error OR a faulty/sticking/intermittent thermostat OR even leaves blocking the radiator/condenser area. The fact you don't have an accompanying SENSOR fault makes me suspect the more fallible thermostat.

The dialog for P0128 reads:

Comparison of actual warm up profile with estimated. Judgement performed when actual ECT reaches 80°C or accumulated difference between actual and estimated coolant temperature reaches threshold.

Which means the ECM estimates what the temp should be with respect to what the startup temp was and how long it's been running, etc. Then it compares that with what the sensor measures.

Cheers,

 

As I said, worth reading the codes PDF. It really is.

 

Thank you all. I was spooked by the different diagnostic. You've set me straight, once again. I'm sure glad there are smart guys around the forum.

 

Excellent info in this thread. My '06 ST VDP had the same EWL and p0128 code (bless Autozone for pulling the code for me). The EWL came on well into a trip and long after the beast was reading normal temp on the dash. The EWL has stayed on for a couple of days.

I presume (suspect) that the thermostat is sticking open or that coolant is bypassing it. I understand that the EWL will clear itself when normal temperature parameters return. I'll be changing out the thermostat. Thanks for the info.

 

Glad we could help.

I suspect your engine temp fell during your drive, and the ECM knew it shouldn't do that. If it were the other way, and your temp rose higher than normal, you would probably notice your fans running a little more than they normally do.

Good luck!

 

EWL is out now, and has been for two days. I now very strongly suspect a sticking thermostat (sticking open intermittently) and will have it changed out, as I'm going out of state the 20th. The last thing I want is to have it stick closed and strand me in the wilds of central Ohio, many miles from help.

 

Good call! I always recommend throwing a thermostat out after two or three years; they are just too cheap to trust for much longer than that. Those things operate based on a wax pellet seeded with a couple of metal powders. Ever wondered why, in this 'electronic' day and age, that they haven't replaced it with something electrical and using temp sensors?? Because they are SO CHEAP!

Good luck!