‘09 Acadia Losing Power, Stabilitrak, Service Light

Hi there. We have an ‘09 GMC Acadia. 131K miles on it.
Back story: Earlier this year when we were in the mountains the check engine light came on. Code read fuel pump control module, low voltage. It was a rainy wet cold day. The next day we cleared the code, and it has only come back on days it starts kinda rough because of cold, etc.
Now: Yesterday was -5 degrees in the morning and had rained the night before. Started the car and the check engine light came on, code reads fuel pump control module. Boyfriend cleared the code and we left for Christmas with my family. Roads are icy the whole way (not sure if this matters). We got about 4 hours into our drive when the dash dings, check engine light comes on, screen flashes “Service Traction Control” “Service Stabilitrak” and “Engine Power is reduced” and eventually engine power is pretty much nothing. When we restart the vehicle it’s fine for another minute or two down the road then happens again.
Code is P0221 & PO121. (Throttle/pedal position sensor switches A & B).
Boyfriend unplugged TPS connector and plugged it back in and it was fine for one day, but we went to leave for home and the same thing happened again.
Do we just need a new Throttle body? I was reading on this issue and it sounds like it can be kind of a gamble between umultiple different sensors/electrical connections that can do this. We just can’t gamble on a million different pets now financially. Hoping someone here can confirm? Thanks y’all.

Neither code points to a problem with the throttle body.

Both both codes point to a problem with the accelerator pedal position sensor.


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“OBD II fault code is defined as “Throttle/Pedal Position Sensor/Switch B Range/Performance”, and set when the PCM (Powertrain Control Module) detects a signal voltage from the TPS (Throttle Position Sensor) that does not correlate with the current engine speed.”

Everywhere I look that code description mentions the Throttle Position Sensor, not the pedal position sensor

Accelerator pedal/throttle pedal.

Six of one, half dozen of the other.



Isn’t there a sensor on the throttle body called the “Throttle Position Sensor?”


Your vehicle has an electronic throttle body.

The throttle pedal position sensor sends a signal to the computer, and the computer operates the electronic throttle body.


The throttle is the part on the engine that opens up to let air in. The accelerator is the pedal you push when you want to go faster. Both of these parts are electronic and each has sensors built into them. The accelerator and the throttle should both match closely when the system is working properly.

P0121 usually indicates trouble with the throttle. P0221 usually indicates trouble with the accelerator pedal. When both are present usually one piece is sending a reading that doesn’t match the other. Should be easy for a mechanic with a decent scan tool to figure out.

Neither of these fault codes should be related to your fuel pump driver codes.

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Just a thought: would it be possible that there is a wiring or connector issue? I’m thinking this because symptoms occured during wet conditions. The connector at the ECM might be bad or reference voltage might be off. I don’t know this cars layout but they might be related.

Does the vehicle have a sunroof?

Just following up, we replaced the throttle body and the problem was fixed! Going on 2 months now, no more problems.

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Just following up in case anyone in the future finds this, we replaced the throttle body and the problem was fixed. Over 2 months now without problems. (Well, without that problem haha)