P0128 after new sensor and thermostat

Von Elling

Well-known member
Joined
Jan 29, 2011
Location
Colorado Springs, CO
TDI
2005 golf gls tdi
Hello everyone,

I appreciate you taking the time to read and address the concerns brought up by us less knowledgeable newbies. So, thank you in advance.

I have an 05 Golf TDI which has a persistent P0128 Code. I replaced both the termostat and coolant temp sensor with no luck. I had autozone clear the code and it came back on immediately upon start-up. What gives?
 

UhOh

Top Post Dawg
Joined
Dec 24, 2014
Location
PNW
TDI
2000 & 2003 Golf GLS (2005 Mercedes E320 CDI)
Did you test the thermostat before installing?

Where did the CTS come from? Crap ones are out there.

Check wiring to the CTS.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Something is not right, as that DTC CANNOT come back immediately after clearing on start up. You need a proper scan tool, as I suspect there is more the ECU can tell you.

In order for that DTC to set, the time stamp and warm up period has to run, and fail, twice, before anything happens. 2-trip detection logic.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Something is not right, as that DTC CANNOT come back immediately after clearing on start up. You need a proper scan tool, as I suspect there is more the ECU can tell you.

In order for that DTC to set, the time stamp and warm up period has to run, and fail, twice, before anything happens. 2-trip detection logic.

You could have a CTS open circuit DTC stored, that would indicate wiring. You can also check what the Instruments says for temp.

Proper scan tools. Worth every penny.
 

jnl_public

Well-known member
Joined
Feb 28, 2009
Location
California, US
TDI
2002 Jetta Wagon
Hey All,


About a month ago, I replaced my ALH's coolant temperature sensor (non-OEM green one). Just this last week, I was able to delete the faults codes with a VCDS. Then, low and behold, the check engine light comes back on a the code thrown is:


16512 - Coolant Thermostat Valve (N214)
P0128 - 35-10 - Temperature below Control Range - Intermittent.


Is there a simple way to check if the issue is with the thermostat?


Thank you as always.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Replace the thermostat. With a new neck and o-ring. I would only use OEM stuff, but if you can source a Behr or Calorstat brand thermostat, those are fine too.
 
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