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Discussion Starter · #1 ·
For a 2001 S40, does anybody have experience with the check the engine light code P0128?
"Coolant temperature below thermostat regulating temperature"

So far:
1. Thermostat was replaced
2. Check engine light was reset

But it keeps coming back after driving a few hundred miles. The next action will be replacing the thermostat again assuming that the recently installed one is defective.

Thanks
 

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we have had the P0128 at least four times on our v40, 2003. it is usually the temp sensor and not the thermostat, although i always replace both and it has always fixed the problem. i have found that the overpriced volvo part is the most reliable and a longer term fix. i have used the $15 part from IPD with success of about two years until the next mil/check engine code. i now buy them (coolant temp sensor) from tasca volvo and keep two on hand. the fix takes 10 minutes and if one leaves the top on the rad fluid tank on, i loose maybe a cup of coolant.

good luck, this is not a hard job at all. ps. make sure you use contact cleaner on the pigtail connector of the temp sensor, i also not use some contact enhancer and wrap the connector with electrical tape as once the problem was corrosion in there. this is from the service adviser at royal volvo san francisco, a long time friend who sees it often on cars near the coast.

again good luck;
 

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Discussion Starter · #3 ·
thank you very much; really appreciate it. Will keep you posted.
 

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DAMN i meant to say i DO us contact enhancer on the contacts!!! i could never spell, or, spell check, sorry i also use tape, and contact cleaner. what we have found is that the connectors are up top on the motor and get much of the convection and condensation that leads to corrosion.

again, now, BEST of luck; jim
 

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Discussion Starter · #6 ·
Saga continues

Thermostat sensor was replaced with the original Volvo part and I gave them the copy of hastee's post above. They followed all the instructions as far as I was told.

After a few months, the check engine light came back for a day but currently it is not active. However, the code reader detects three codes:
- p0128
- p0128 (pd)
- p0130 (sensor circuit malfunction (bank 1 sensor 1)

As the light is off now, I am ignoring these codes but wanted to get your thoughts too if you don't mind
thanks
 
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