94 K1500

RAZOR

Senior Member
Location
Ontario, Canada
The "Sevice Engine Soon" light is coming on, when it does the engine revs high before shifting hard into the higher gear. It is showing a code #12. It only seems to do this when the truck is cold, when it warms up it is fine. Does anyone know what a code 12 is?

Thanks Razor
 

JohnnyU

2000 Club Member
this code will flash when ever the diagnostic terminal is grounded with the ignition turned on and the engine not running. If additional trouble codes are stored in the ECM they will appear after this code has flashed three times.

I read that from my service manual, sounds like its not throwing any codes, check again after this code 12 has flashed three times.

John
 
OP
RAZOR

RAZOR

Senior Member
Location
Ontario, Canada
Thanks for the reply,I checked it again, after it flashed code 12 three times it flashed code 22, It looks like it might be the Thottle Position Sensor.

Razor
 
code 22 is the TP sensor voltage too low.Sounds like a bad TP sensor.Disconnect the sensor and jump the blue and grey wire and it should set a code 21.If it does it's a bad TP sensor.If not it's wiring or ECM related.

While your in there check the base gasket for the TBI unit,as they are bad for cracking and causing a high idle as well.
 

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