Speedometer jumping car bogs down at sixty mph

LSTALEY

MEMBER
2001 CHEVROLET SUBURBAN
5.7L
V8
4WD
AUTOMATIC
200,000 MILES

After travelling on highway for about five minutes around sixty mph the Speedometer will drop to forty or fifty and jump drastically. Rpm go to about 3000 then drop and car bogs a little but will still go and shift.

Tuesday, March 13th, 2018 AT 4:46 PM

7 Replies

ASEMASTER6371

MECHANIC
52,797 POSTS

Good morning.

When the speedometer changes speed, does the trucks speed change or does it maintain speed?

Roy

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Wednesday, March 14th, 2018 AT 5:14 AM

LSTALEY

MEMBER
4 POSTS

It bogs just a little but will maintain speed and will accelerate even when speedometer is floating.

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Wednesday, March 14th, 2018 AT 6:45 AM

ASEMASTER6371

MECHANIC
52,797 POSTS

Okay, there is a speed sensor at the transmission that sends a signal to the PCM and that signal is transferred to the dash.

You need a scan tool to monitor this signal to see if the signal is steady or if it is lost in transferring between modules. It can also cause the bogging as it controls transmission up shifts and downshifts as well.

Do you have a scan tool?

Roy

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Wednesday, March 14th, 2018 AT 6:48 AM

LSTALEY

MEMBER
4 POSTS

No I do not.

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Wednesday, March 14th, 2018 AT 12:45 PM

ASEMASTER6371

MECHANIC
52,797 POSTS

If you cannot get one, see if a shop can check it for you to be sure the signal is getting to where it needs. If it does need the sensor, you can do that part of the job.

Roy