The Strangest Transmission Problem I've Ever Encountered

tightmopedman9 · Post by **tightmopedman9** » 12 Mar 2021, 12:43

Short version of the story:
2005 XC90 occasionally shifts so poorly it won't move. The shift lock solenoid in the gear selector pulses rapidly when in park and the key in POSII or engine running. Sometimes the car will shift perfectly fine for up to 4 miles. Sometimes I can't even get the car back up the driveway after only running for a few minutes. I have replaced the valve body, then the transmission. I have tried a new TCM, cloned the CEM, a new BCM and a used GSM. Nothing has changed the issue. I have noticed that the DIM doesn't always show the correct position of the GSM. If I start the car and the shift lock solenoid isn't pulsing the car will garage shift smoothly. If the shift lock solenoid is pulsing, then the transmission will garage shift extremely hard.

Long version of the story:
I run a small shop that specializes in Volvos, mostly P2s. A customer came in with a 200k XC90 for a pre-buy inspection. Car looked clean and well maintained, and considering the low price I thought it would be a good purchase. I did $1000 worth of work to the car immediately after purchase, including a 14L transmission flush. After 300 miles and two weeks of driving the customer called me and said that the car had started bucking so violently while driving that they hurt their neck. The car was towed to my shop and I test drove it. For 4 miles of driving it shifted totally fine, then while accelerating after a low speed turn the car started bucking violently. It felt almost like it was rapidly shifting between 1st and 2nd. I informed the customer that there was a possibility a new valve body could fix the problem, but most likely it would need a new or rebuilt transmission. They declined the service and the car sat in front of my shop for 6 months. I purchased the car from them in the hopes that a new valve body would fix the problem and I could have a good car for my girlfriend.

Before replacing the valve body I test drove the car and tried resetting adaptations through VIDA. I noticed after getting in the car that the shift lock solenoid would rapidly pulse while in park, when the engine was running or the key in POSII. The transmission shifted very hard from P->R and P->D and immediately exhibited the same jerking shifting.

I replaced the valve body with a new ACDelco/GM unit, something I've done many times before. When I got back in the car to test drive, it exhibited typical CEM failure symptoms - flashing lights, clicking door lock actuators, no communication through VIDA and I could hear solenoids in the valve body clicking. I charged the battery overnight, and it appeared the CEM was no longer bad, so I assumed it was just a low voltage issue. I test drove the car and it still shifted harshly from P->R and P->D. It drove and shifted OK for 4.6 miles, then started shifting poorly again. I took the valve body out, put the old valve body in and the test drive was exactly the same. I put the new valve body that had been in the XC90 in my personal XC70 and the XC70 shifted like new, when previously it shifted so poorly it was almost undriveable.

I ended up replacing the transmission with one from a local independent Volvo shop. It had sat in a shipping container for years so they didn't know the exact condition of it, but it said 86k on it. I am friends with the owner of the shop and he just gave me the transmission, so I know that the mileage on it was accurate. I also replaced the valve body with a new ACDelco unit. After putting this new transmission in the XC90 the shifting issue was more or less the same. The car drove fine for 4 miles, then seemingly went into limp mode. However, even though it seemed that when starting from a stop the transmission was in 3rd, at around 15MPH the transmission shifted extremely hard into 2nd gear.

I cloned the CEM, thinking that maybe the TCM was getting incorrect information and making poor shifting decisions. I once had another 2005 XC90 in shop for a CEM repair and before the CEM was replaced the shift lock solenoid was pulsing rapidly. Once the CEM was replaced the shift lock solenoid no longer pulsed. After cloning the CEM on my XC90 the car shifted beautifully, better than it ever had. I drove it for 1.5 miles and thought the problem was fixed. I drove the car the next day and after 2 miles it shifted once very hard from 1 -> 2. After another 2 miles of driving the car started jerking violently. I came to a stop and couldn't even drive the car a 1/4 mile of the way home.

Since then I have replaced the BCM, GSM and TCM. Nothing has changed the issue. I have worked on 200 or more of these cars and have never experienced a transmission failure like this - what is the likelihood that the new transmission I put in the car had the same exact issue as this one? I feel that it is an electrical issue, but I'm not sure how that could be the case since I've replaced every relevant module. I'm going to do some wire tracing and make sure the wiring and grounds are good.

Post by **MoVolvos** » 12 Mar 2021, 13:44

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Terrible with electrical or electronics but before finishing reading I was thinking grounds or perhaps a pinched / weak wiring somewhere. Install a new battery also.

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Post by **cn90** » 12 Mar 2021, 17:19

- Check ground wires.

- Check for any wires chewed by squirrels/rats etc.

Post by **RickHaleParker** » 13 Mar 2021, 01:10

I do not see Gear selector switches on the list of things you have tried. The Gear selector is a switch mounted on the transmission and controlled by the gear select cable. Not the GSM which is inside the car AKA as the Stick Shifter.

Did you transfer the Gear selector from one transmission to the other or did the replacement transmission come with a gear selector on it?

Have you tired running through the gears in manual mode?

Is it throwing any Diagnostic Trouble Codes (DTCs) after a hard shift?

How is you battery condition? Low voltage can cause all kinds of shifting problems. When I first got my 2005 XC90 T6 it has a stew of shifting problems until I dealt with the battery. After dealing with the battery. It still hard shifted one in a while. I seems to have worked itself out. I have not had a hard shift in some time.

Sift solenoid #1, #2 and lockup have a common ground. If the ground was bad it would effect all three.

tightmopedman9 · Post by **tightmopedman9** » 18 Mar 2021, 21:16

I must admit, I am quite embarrassed by what the cause of the problem was - so much so that I thought about not posting a follow up to this thread. However, I want this information to be known so that this problem doesn't cause anyone else the grief it caused me.

I started checking grounds and the wiring harness at the transmission and couldn't find any problems. I went in the car and checked voltage at the GSM and found only 9V, even when running. Voltage at fuse 21 (supply to GSM) was good, but voltage between the GSM's ground and battery voltage was still only 9v. The GSM gets its ground from the chassis at 31/94 through the TCM. I went in the engine bay to check the wiring at the TCM socket and as soon as I started to pull the TCM out I noticed the 10mm bolt for the ground connection next to the ECM/TCM box was loose. Tightened that bolt up and no more issues.

I have no idea why this bolt was loose. I never touched it and I have no idea why anyone would ever mess with it.

Anyways, at least the car now has a low mileage transmission, a new RMS and a fresh collar sleeve.

Thanks for the ideas everyone!

Post by **MoVolvos** » 18 Mar 2021, 21:26

tightmopedman9 wrote: ↑18 Mar 2021, 21:16 I must admit, I am quite embarrassed by what the cause of the problem was - so much so that I thought about not posting a follow up to this thread. However, I want this information to be known so that this problem doesn't cause anyone else the grief it caused me.

I started checking grounds and the wiring harness at the transmission and couldn't find any problems. I went in the car and checked voltage at the GSM and found only 9V, even when running. Voltage at fuse 21 (supply to GSM) was good, but voltage between the GSM's ground and battery voltage was still only 9v. The GSM gets its ground from the chassis at 31/94 through the TCM. I went in the engine bay to check the wiring at the TCM socket and as soon as I started to pull the TCM out I noticed the 10mm bolt for the ground connection next to the ECM/TCM box was loose. Tightened that bolt up and no more issues.

I have no idea why this bolt was loose. I never touched it and I have no idea why anyone would ever mess with it.

Anyways, at least the car now has a low mileage transmission, a new RMS and a fresh collar sleeve.

Thanks for the ideas everyone!

Good to know it was something simple. We all miss the simple stuff and there are so many grounds sometimes you really don't know where to start unless you have a diagram.

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Post by **ZionXIX** » 18 Mar 2021, 22:21

I still can't locate all the grounds even with the diagram. Engineers seem to take it as a personal challenge to hide them.

Post by **abscate** » 23 Mar 2021, 03:55

A car that changed hands three times because if a loose bolt. It pays to go back to basics!!

Jimmicorn2 · Post by **Jimmicorn2** » 17 May 2021, 21:10

Damn sounds like I need to start checking grounds as well. Just had the Dim rebuilt thought I'd start there since everything started to go at once after trying to reset my dash clock. Damn day light savings. Never depress those sticks on your dim. Never never

Post by **oragex** » 18 May 2021, 06:38

abscate wrote: ↑23 Mar 2021, 03:55 A car that changed hands three times because if a loose bolt. It pays to go back to basics!!

Imagine having walked into the dealership. $5000 dollars later you discover it was a loose bolt
Was this one of the three bolts by the side of the engine bay near the hood line ?