2004 GMC Envoy P0128 and Losing Coolant

Tiny
ADLPN
  • MEMBER
  • 2004 GMC ENVOY
  • 4.2L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 140,000 MILES
I bought the envoy a couple months ago with the only known problem being the ac resistor (a/c only ran on 1 and 5) fixed that
Then the battery kept dying
With bad battery I noticed it seemed to surge slightly when going and when idle rpms drop from 600 to 400 when ac or defrost is on.
Replaced the battery and now it will die if you idle with ac on.
SES light was on when I bought it so I got the code P0128
Engine temp never rises above 160-180 on the gauge
Also noticed I keep filling the overflow reservoir with Dex Cool and it disappears (not sure how long it takes to empty) The radiator is full.
After looking the coolant is constantly dripping from the overflow tube into the passenger fender well.
Plans are to change the thermostat (and temp sensor while I'm there) and clean the throttle body.
My question is could the problems be connected and Why would the coolant leak from the overflow with reservoir empty with car cold or hot running or not.
Do you
have the same problem?
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No
Wednesday, January 15th, 2014 AT 11:48 AM

4 Replies

Tiny
SATURNTECH9
  • MEMBER
For the p0128 you have a bad thermostat very common on the gm vechiles. As far as the coolant dripping from the over flow I would say you have a bad radiator cap. Not holding pressure then the smallest pressure it leak coolant like its overheating.
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Wednesday, January 15th, 2014 AT 12:04 PM
Tiny
HMAC300
  • EXPERT
Have the coolant system pressure checked for leaks like a head gasket. I have seenon tips page replacing tstat and map sensor to get rid of 128 code. You might also try cleaning throttle plate an diac hole with choke cleaner seems to help those.
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Wednesday, January 15th, 2014 AT 12:05 PM
Tiny
SATURNTECH9
  • MEMBER
Also simple bad cap will cause the coolant to come over the cap. Never seen a map sensor set a p0128 on a gm vechile its usually the thermostat.
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Wednesday, January 15th, 2014 AT 1:46 PM
Tiny
ADLPN
  • MEMBER
(for anyone else with these problems)
The idle problem was a dirty throttle body
The thermostat was stuck open
Changed the radiator cap but still leaking from overfill so the search is still on for that one.
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Sunday, January 19th, 2014 AT 11:04 AM

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