No 4th gear

[Bonneville'n]

I've been having issues with me transmission shifting into 4th gear. It will shift into 4th gear initially before the car warms up, but once it does it loses 4th gear altogether. Any ideas? Thanks for any help.

[Bonneville'n]

This all started when I was driving in a torrential downpour a couple of months ago. It lost 4th gear driving to work. Ever since then it slowly got worse happing more and more, now it happens every time. It does still shift initially when cold, so I know it works. I'm thinking something electrical?

[Luxrain]

To be honest I agree with ya. Hopefully one of the techs will pop in and may have more info for ya

[michtom]

Are you checking your transmission fluid level when it is at operating temperature? Also does it have a burnt smell?

[Bonneville'n]

Transmission fluid is full when hot no smell...I had it to a transmission shop. He said it all looks fine on his tests. His suggestion was a bad pcm or ground, I have got a new intense pcm...still no 4th gear.

[michtom]

The only thing I can tell you to check is the input switch c for a open or bad connection. That would be a gray wire from the transmission connector terminal H that goes to the pcm connector 2 terminal 56.

[MKMike]

Next thing to do is to check and see if the computer has stored any codes.
They may at least hint at the cause.

The PCM uses engine and transmission sensors to operate the transmission, so the problem can be electrical or mechanical.

As the transmission shop mechanic suggested, it would also be wise to clean as many ground connections as possible.

[Bonneville'n]

I was driving home today and the transmission was shifting hard...I ran it for codes, saw P1810. It shifted hard the whole way home but shifted into 4th gear for the whole ride. Bad solenoids?

[MKMike]

Start at the cheapest things first---clean up all the grounds.
The PCM requires accurate info from the sensors in order to properly operate the transmission solenoids.
If the PCM believes that the engine isn't warmed up enough, for example, then it will not engage 4th gear.
I have read of a faulty TPS causing the lack of 4th gear. Same for bad ECT sensor.

There is also a TSB which tells technicians to carefully check the 20 pin connection to the tranny--check for breaks in the wiring where the cable runs next to things and check both ends and all connections.

Bad transmission mounts have been known to wreak havoc, too, since the excessive motion can strain the connector.
Loose pins, corrosion, etc. will cause problems.

Ignition issues are another possibility, as they can mimic transmission troubles.

Seems that it will likely take time and probably an advanced scan tool (Tech 2) to pinpoint the issue.

Update: Found the post with the TSB.
http://www.pontiacbonnevilleclub.com/fo ... 26128.html

[Roadrunner]

Common problem (been there)
http://tripleedgeperformance.com/No-4th-Gear.html

[MKMike]

Common problem (been there)
http://tripleedgeperformance.com/No-4th-Gear.html

Would the worn off splines cause intermittent engagement in 4th?
If so, any idea why it would engage flawlessly until fully warmed up?
I've read of the worn spline issue but thought if it was a sudden complete loss of 4th.
Does if it instead present as an intermittent, increasingly frequent problem that first is noticed when the car is fully warmed up?

Seeking to increase knowledge ; not doubting veracity.

[dougtoth]

I know on my 2000 Bonneville SLE when I lost 4th gear it as all the time.
I had the transmission rebuilt ($1800.00) because of the soft spline.(125,000 miles at the time)
The shop showed me the part and is was almost completely smooth.(splines were gone)
I would like to again thank GM for this screw up.