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1997 GMC Suburban 5.7L 2WD 1/2 Ton P0122 and P1122 Codes - Hard Shift & SES Light On

Model: 97 Suburban 5.7 2-wheel drive 1/2 ton Fault Code: P0122 Posted: 2007-06-25 18:10

I recently purchased a 1997 GMC Suburban with a 5.7L V8 engine, 2-wheel drive, 1/2-ton payload capacity, and a tow package. The vehicle has accumulated 165,000 miles. After replacing the intake gaskets and upgrading the fuel injection unit, it runs smoothly. However, over the weekend, while towing a small load of branches to a dump, I experienced an unusually hard shift from first to second gear. At that moment, the SES (Service Engine Soon) light illuminated. After dropping off the trailer and shutting down the vehicle, I restarted it — at which point the SES light was no longer on. I then took the truck to Avance Auto for a diagnostic scan, which revealed two trouble codes: P0122 (Throttle Position Sensor 'A' Circuit Low Input) and P1122 (Throttle Position Sensor 'A' Intermittent Circuit Low Voltage). The issue has not recurred since. I'm wondering if these two codes are related to the hard shift I experienced during towing. Given that the throttle position sensor (TPS) is a critical component in engine control, could a faulty TPS be causing transmission shifting issues? A new TPS unit costs less than $50. Should I replace it as a fix, or might this be unrelated to the shifting problem? Any insights would be greatly appreciated. ccnova

Related fault codes
P0122P1122
Comments (6)
Anonymous 2007-06-26 06:47

Could the hard shift be related to having the trailer connected or increased load on the vehicle? The extra weight might affect transmission behavior.

Anonymous 2007-06-26 07:45

I’ve read that the throttle position sensor (TPS) plays a vital role in engine performance and transmission shifting. If it's not functioning correctly, it could indeed impact gear transitions. Is this accurate? Thanks for the input, ccnova.

Anonymous 2007-06-26 10:14

It’s possible — but likely just a coincidence. A TPS sensor is relatively inexpensive to replace; if you're considering a fix, it might be worth trying as a simple and cost-effective step.

Anonymous 2007-06-26 17:44

I hadn’t connected the two issues before — I just thought it was bad luck having multiple problems at once. Still, I’m hesitant to replace parts without proper diagnosis. Is there a better way to investigate this issue beyond guessing?

Anonymous 2007-06-27 06:37

Using an oscilloscope to monitor the TPS signal would provide clearer insight into whether the sensor is sending accurate data.

Anonymous 2007-06-27 16:48

I don’t have access to a scope right now. I’ll probably go ahead and replace the TPS as a temporary fix, hoping it resolves both the code and shifting issue. Thanks for the help, ccnova.