2003 Pontiac Bonneville Clunks hard into gear at low speeds

NOTAPROMIKE

MEMBER
2003 PONTIAC BONNEVILLE
6 CYL
FWD
AUTOMATIC
90,000 MILES

I sold a friend this car with 70k miles on it. Now, at 90k, it has developed a problem at low speeds only. When stopping or starting it comes out of gear and then slams back into gear quite roughly. He had it diagnosed @ 3 different transmission shops, all 3 told him it was the pressure control solenoid with an estimated repair cost of $300.00 to $1800.00. He elected to have a shop fix it for 400. Repairing the solenoid only. When done, the shop told him it is better, but still does it and they suspect it may be the throttle positioning sensor. If so, I would suspect that the problem was the TPS all along, NOT the transmission. What is your opinion on this? The shop still has the car and it is still not fixed. What could be cusing this and how can 3 shops incorrectly diagnose a problem?

1 Reply

DENNYP

MECHANIC
1,823 POSTS

Have them scan it for trouble codes. You will probably find a P1811 for max shift adapt.
This code is normally caused from a bad PC solenoid or binding pressure control valve in the valve body.
I have also seen excessive debris in the trans fluid cause this.
I would recommend flushing the transmission with a flushing machine, then remove the valve body to disassemble and clean the valves and bores.
Also, check the pressure range switch for excessive debris buildup in the switch pads.