Transmission or ignition coils
Asked by Honeybadger42x Dec 06, 2020 at 08:50 PM about the 2003 Pontiac Grand Prix GTP
Question type: Maintenance & Repair
On my 2003 pontiac gtp supercharged the Transmission
shifts hard or late when warm, acceleration is slow, mpg
has dropped from 20 to 9. I've heard it can be the fuel
pump, the coils or the transmission, ant idea what I should
go towards first, already had a fuel pressure issui a couple
years ago so fuel pump has already been replaced before.
4 Answers
You have multiple issues. Take it to a transmission shop and then to a mechanic for a tune up and diagnosis.
Check shift solenoids, might need a transmission flush, as old transmission fluid burns up it can gum up the lines to the shift solenoids causing hard/delayed/no shift, as for mpg, I would start by checking evap system lines and vacuum lines
These transmissions are known for losing overdrive and TCC lock in. There's a shaft in the transmission that wasn't hardened properly at the factory and the splines break off. This will cause your symptoms. The service engine soon light will not come on because the PCM thinks the upshift to overdrive and TCC lock in has occurred, when it has not. It can be repaired by a reputable transmission shop for around $1,500. Hope that helps! Jim
I see lots of good advice here. My only addition would be to do your trouble shooting first, then start buying parts or doing repairs, That way you're only spending money on what really needs fixing.... bearing in mind its an old car with very little value, so don't get too carried away if its actually time for a different car. Just my 2 cents worth.
