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Transmission slams moving to reverse or drive, possibly self inflicted


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btah
User

Aug 6, 2016, 1:58 PM

Post #1 of 25 (1728 views)
Transmission slams moving to reverse or drive, possibly self inflicted Sign In

Hoping I can get some direction from a trans expert.

Here is the story. 2002 Grand Am GT, 140,000 miles, motor is the 3400. My son got the car a few months ago and we got screwed. The car uses a quart of oil every 350-ish miles. Over the weekend I tried the old school trick of introducing some Borax through the air intake to reseat the rings. Then the problem started about 10 miles after doing the procedure.

Shifting into drive or reverse is more like a slam. And I mean slam, like someone jumped on the car. Also, hard shifts into all gears while driving. I did replace the front and rear trans mounts because they were not in good shape. No difference to my problem. Not engine light on.

However, I have found that if I unhook the battery for 10-15 minutes and then hook it back up, the car will act perfectly normal for maybe 5 or 10 minutes. Then the slamming and hard shifting comes back.

I talked to a trans shop this morning and his first words were that some sensor is telling the trans it needs to be at full pressure.

I don't know how the sensors affect the transmission.

Can any of you trans experts help me out?


Thanks ahead of time...


kev2
Veteran
kev2 profile image

Aug 6, 2016, 2:22 PM

Post #2 of 25 (1720 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

scan the vehicle for codes- especially if the light is off.
post ALL codes and someone will advise..


Do you have any idea where oil is going - leaking, consuming would surely produce a black exhaust... yes ?
you might want to do a compression test - the comparative readings also you could observe the condition of plugs might help ID the problem cylinder AND with plugs out crank engine over to blow out any BORAX solution...
Any evidence of oil in coolant?
How did you introduce the borax solution into engine?


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Aug 6, 2016, 3:47 PM

Post #3 of 25 (1713 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

Borax? How about some Soft Scrub? Nothing like Borax all over the MAF sensor elements and O2 sensors. Wonder how the catalyst likes Borax? Can't believe people fall for that stuff.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Aug 6, 2016, 3:48 PM)


btah
User

Aug 6, 2016, 5:06 PM

Post #4 of 25 (1708 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

The Borax thing has been around a very, very long time. Talk to some old GM mechanics and they can probably tell you all about it. MAF sensor is before the throttle body so that isn't an issue. O2 sensors are clean. Soft Scrub is too harsh... But, thanks for the input.


btah
User

Aug 6, 2016, 5:15 PM

Post #5 of 25 (1706 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

The oil is being burnt, obvious via the exhaust. Burning about a quart every 350-ish miles. No oil in the coolant.

I don't want to get caught up with the oil burning issue though. I will continue to deal with that after I get the trans straightened out. I no longer see smoke coming out of the exhaust but I am hesitant to drive the car because of the trans issue. Just to finish off your question though, you remove the air plenum and let the borax suck slowing into the throttle body.

I will have to take it to a shop this week in order to get the codes read. No easily accessible (meaning for free and open weekends) place will read trans codes. The plugs and O2 sensors are clean. I have also checked the MAP sensor which is attached to the intake manifold (and the only sensor I can see that is in the path) and it appears to be operating properly.

I do appreciate your input.


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Aug 6, 2016, 5:27 PM

Post #6 of 25 (1703 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

MAP sensor isn't going to cause your harsh shifting issue. The MAP is used by the engine computer as a back up if the MAF sensor has a fault. It is also used to measure the BARO pressure.

The two main sensors that affect transmission line pressure are the TPS and the MAF sensor.

If borax was used in the past, it sure isn't done today in the industry that I have seen. There is no manufacture procedure in the service information for correcting oil consumption issues using borax. You will eventually need to figure out why your engine is burning so much oil because the catalyst and O2s are getting poisoned. I really don't think that borax is going to solve anything if you have valve stem seal or guide problems. Borax isn't going to restore broken rings, worn out rings, or worn out cylinder bores.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


btah
User

Aug 6, 2016, 5:38 PM

Post #7 of 25 (1701 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

Thanks. The tps checks out ok by checking it with a multimeter for whatever that is worth. I have unhooked the Maf and the car runs bad so it seems like it is working properly. I was thinking a bad Maf would throw a code.


Discretesignals
Ultimate Carjunky / Moderator
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Aug 6, 2016, 5:46 PM

Post #8 of 25 (1698 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

Faulty MAF doesn't always set codes. Kevin's suggestion of seeing if there are any trouble codes stored is a good suggestion. You'll probably see circuit codes stored for any sensors you may have unplugged with the key on or engine running. You may need to clear codes and drive again with everything hooked up to get an accurate code reading.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


btah
User

Aug 6, 2016, 5:53 PM

Post #9 of 25 (1696 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

I unhooked the battery for about 1/2 hour and all the light I had on from when I was unhooking the sensors has gone off.

I still think the oddest thing is that for a while after hooking the battery back up the car will be fine. Does that rule out the trans' internal pressure sensor? I would think that would be stuck one way or the other and not go back and forth.


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Aug 6, 2016, 6:08 PM

Post #10 of 25 (1692 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

There may be a fault causing the PCM to default to high line pressure. Should be trouble codes stored if that is the case. I don't think the PCM has any feedback to the actual line pressure inside the transmission. It is able to calculate what the line pressure should be based off engine sensor inputs, look up tables, and shift adapts, but other than that it is blind to the actual amount of pressure that is happening. Gary would know more about that sort of thing. Code reading should be your next step.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


btah
User

Aug 6, 2016, 6:17 PM

Post #11 of 25 (1688 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

Thank you


gsferraro
Veteran

Aug 6, 2016, 6:24 PM

Post #12 of 25 (1683 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

Hello,
Scan for codes thats a must, also has the fluid level been checked, this trans should be a 4T40E, no dipstick has to be put on a lift to check the fluid level. Gary


btah
User

Aug 6, 2016, 6:48 PM

Post #13 of 25 (1681 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

Fluid was a about a half quart low, first thing I checked


btah
User

Aug 7, 2016, 9:32 AM

Post #14 of 25 (1661 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

Well, I found something that might point in a direction. After the post about the MAF affecting the trans I did a voltage test on the signal wire. I understand from looking at some other stuff on the all-knowing internet that voltage is not the best way to test but that is all I have. I don't have a meter that tests in hertz.

Anyway, at idle with the car warmed up I get a reading of 4.4 volts DC on the signal wire. Increasing the throttle actually makes the volts go down a little. I brought it down to 3.8 volts by increasing the RPMs and stopped there.

I tested my other son's grand prix and his idle voltage was like 2.6 or something like that and increased a little as I increased the RPMs.

Does this point to a bad MAF making the motor think I am screaming down the highways and puts the trans into high pressure mode?


kev2
Veteran
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Aug 7, 2016, 9:34 AM

Post #15 of 25 (1661 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

FOCUS: trans first
Codes are the starting place, you will likely see MAP, MAF, or TPS issues... causing the line pressure issue.
MIght want to get familiar with their location, R&R etc. If I were to suggest somewhere to start MAP and vacuum leaks...get a can of MAF cleaner while at store for code reading.


The ring seating issue we can address after we do trans. Today There are better options than the old school tricks.


btah
User

Aug 7, 2016, 9:58 AM

Post #16 of 25 (1659 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

No place open on the weekends to get the codes read.

Based on a comment you made yesterday about the MAF and TPS affecting the trans I checked the MAF with the tools I have. I previously checked the TPS to see if the voltage moved with the throttle movement, and it did. I am familiar with all the other sensors. They all have been cleaned/checked as far as I could with a multimeter.

Forgetting everything else, the MAF gets a 12 volt input and returns some voltage through the signal wire. That seems self contained to me and could only be affected by the MAF itself. Given that it seems to always be returning almost maximum voltage, that seems like a problem irregardless of any other issue going on. Am I thinking about that incorrectly?


btah
User

Aug 7, 2016, 10:09 AM

Post #17 of 25 (1654 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

Sorry, Discretsignals mentioned the MAF sensor.


kev2
Veteran
kev2 profile image

Aug 7, 2016, 2:18 PM

Post #18 of 25 (1638 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

this is a 3 wire maf? red or pink 12v, Brn or blk center wire is ground, the white wire is signal return- the signal is reported as a HERTZ Frequency.


have you looked at MAP sensor? KOEO what is V on cetere wire ? then with engine idling what is V on center wire lt/grn?


(This post was edited by kev2 on Aug 8, 2016, 11:43 AM)


btah
User

Aug 7, 2016, 3:10 PM

Post #19 of 25 (1634 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

KOEO 4.75v
idle 1.35-ish (bounces around a little)

A little more information. I had to go to the boneyard today for something totally unrelated. I grabbed a MAF, TPS, IAT, and MAP sensor while I was there. No difference with those installed although it is very possible I got bad sensors... The original MAP and the boneyard MAP have pretty much the same voltages.

Dropping it off at a shop tomorrow.


btah
User

Aug 7, 2016, 3:12 PM

Post #20 of 25 (1633 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

And, I have never seen KOEO before but I assumed it meant Key on engine off.


btah
User

Aug 8, 2016, 5:10 PM

Post #21 of 25 (1609 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

solved

I will go with "partially" self inflicted. One of the wires for the IAT sensor was damaged in the wiring harness about 10 inches away from the sensor. It must have been barely hanging on and with me moving the plenum/wires around I finally killed it. Wire repaired, problem solved.

Thanks to everyone that chimed in.

I'll post back in a few weeks just to let you know if the borax did me any good...


btah
User

Aug 8, 2016, 5:22 PM

Post #22 of 25 (1606 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

Actually, if someone could piece this together for me I would appreciate it. If I remember correctly, the mechanic said it was sensing something like 38 below zero. I could have possibly heard him wrong though. Anyway, without the IAT sensor working, anyone know the reasoning behind putting the trans in high pressure mode?


gsferraro
Veteran

Aug 9, 2016, 3:34 PM

Post #23 of 25 (1593 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

This is all computer strategy, when the computer sees something it shouldnt or it doesnt like, it may raise the line pressure of the trans to save it from possible damage. A bad running engine or certain engine codes affect transmission operation. Gary


btah
User

Aug 9, 2016, 3:42 PM

Post #24 of 25 (1591 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

So, I'm curious. Long term it can't be good for a transmission to always have the high line pressure. How long before something bad happens. Are we talking hundreds, thousands, tens of thousands of miles?


gsferraro
Veteran

Aug 11, 2016, 4:37 PM

Post #25 of 25 (1563 views)
Re: Transmission slams moving to reverse or drive, possibly self inflicted Sign In

Hello,
No high pressure is not good all the time. Cant really say how long it will last, but the computer is programmed to raise line pressure if it sees the trans starting to slip(raises it about 10 psi) but if it keeps seeing something it will keep raising the line pressure upto about 30 psi before it flags a code. ive seen drums break and bands snap because of high pressure. Gary






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