Transmission not shifting properly

JOEL SEDAM

MEMBER
2003 GMC ENVOY
4.2L
6 CYL
4WD
AUTOMATIC
175,000 MILES

I did a filter service on my vehicle six months ago. Now it does not want to shift properly. It goes to 4,000 rpm to shift from first to second. Same for second to third gear. As you give it gas to pass somebody it acts like it drops out of gear and loses all power. Then you have to baby the throttle just to get it over 40 miles per hour. I changed the 1 2 and 2 3 shift solenoids as well as the vehicle speed sensor on the output shaft of the transfer case. I still cannot get it to shift properly and do not want to resort to taking it to a dealer just yet. Do you guys have any other options?

7 Replies

ASEMASTER6371

MECHANIC
52,797 POSTS

Good afternoon,

The dealer is the last place you go. Go find an independent transmission shop who will properly diagnose it and repair it rather than just charge you $200.00 and tell you it needs a transmission.

As far as the shifting, the TPS or throttle position sensor is what controls shift times. I would have that checked to be sure the proper voltage signal is being sent to the PCM.

Is the check engine light on? If it is, do you know the codes?

Roy

https://www.2carpros.com/articles/automatic-transmission-problems

The throttle body assembly consists of the throttle body, the throttle position (TP) sensors, and the throttle actuator motor. The throttle body functions similar to a similar to a conventional throttle body with the following exceptions:
- An electric motor opens and closes the throttle valve.
- The throttle blade is spring loaded in both directions and the default position is slightly open.
- There are two individual TP sensors within the throttle body assembly.

The TP sensors 1 and 2 are potentiometer type sensors each with 3 circuits:
- A 5-volt reference circuit
- A low reference circuit
- A signal circuit

The TP sensors are used to determine the throttle plate angle. The control module provides each TP sensor a 5-volt reference circuit and a low reference circuit. The TP sensors then provide the control module with signal voltage proportional to throttle plate movement. Both TP sensor signal voltages are low at closed throttle and increase as the throttle opens.

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Friday, November 23rd, 2018 AT 2:37 PM

JOEL SEDAM

MEMBER
4 POSTS

Thank you, I will try that. Now the only codes in the computer were a u1000 and a C 0 3 0 0 for the rear prop shaft position sensor and O2 sensor burning rich bank 1 sensor 1 and I just had the bank 1 sensor 1 O2 sensor replaced.

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Friday, November 23rd, 2018 AT 3:11 PM

ASEMASTER6371

MECHANIC
52,797 POSTS

You are welcome.

Always glad to help.

Keep us updated with the results.

Roy

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Friday, November 23rd, 2018 AT 3:18 PM

JOEL SEDAM

MEMBER
4 POSTS

Well it still does not want to shift properly but here is something new I found. What controls the fuel economy and instant fuel economy on the gauge cluster? Because they both are registering zero even while driving.

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Saturday, November 24th, 2018 AT 8:00 AM

ASEMASTER6371

MECHANIC
52,797 POSTS

What did you try? Was something done that you say it still will not shift?

No, that is a separate issue. It works off engine vacuum to the map sensor.

Roy