2003 XC70 - unable to get rid of P0740 code

badcadman · Post by **badcadman** » 15 Feb 2016, 20:32

I have a 2003 XC70 that was showing symptoms of the typical transmission failure common to the AW55-51. It all started shortly after I purchased the car in August, with rough shifting up/down. I performed the trans flush and things seemed to calm down for a couple of months, ~500miles. This puts me in December, roughly 166,000miles on the odometer. Fast forward to the holiday break when I go to perform some basic maintenance on the car, and when pulling into the garage it was barely moving. In drive the car would rev to ~4000rpm and barely move. At this point I'm realizing the end is near, and start heavily researching what was coming up next. A few days later while driving the car I get the "Transmission Service Required" warning and CEL's start posting to the computer. The car shuddered heavily when the code posted, and locked the trans into 4th gear. I nursed it the rest of the way to the office, shut the car off, re-started and found I was able to get the car back into normal drive mode, as well as use the manual shifting mode.

Checking the codes resulted in P0700 and P0740. P0740 is correlates with torque converter lockup not possible, i.e. slipping. I take the car to a trans shop in the area that is familiar with the issues posed by these transmissions, and I agree to get a rebuild. After quite a large bill I have a new torque convertor, clutch steels, clutch wear surfaces, clutch band, light valve body rebuild ala "shift kit", and of course a full fluid flush. The old components from the trans showed extreme wear, so all seemed to be pointing to the possibility of success. Before the car was back in my possession, the shop owner takes the car for a test drive to verify correct operation of the trans, and the P0740 code with the corresponding shudder and lock into 4th gear occurs. He clears the code when back at the shop and lets me know the mediocre news. I chance it, pick up the car as I need transportation (after not having a car for a week and a half) and try to limp the car in manual mode as I did previously for a couple of weeks. A couple of miles after I picked up the car it throws the code P0740 again. I return the car to the shop the following afternoon, this time with no reverse, 1st or 2nd gears. Loss of the gears was due to an assembly issue that thankfully didn't frag any of the internals...but this means out with the trans for the second time.

Now on to finding a valve body...I find a supplier in Canada that has OEM valve bodies at far more reasonable prices than any of the local indie or Volvo dealers are quoting. I purchase the valve body on Monday, have it drop shipped to the trans shop who receives it later that week on Friday, with a physically broken torque convertor lockup solenoid. At this point I'm ready to puke, as I'm north of $3500 in a trans rebuild + parts, and we haven't even pulled the trans back out to work on the valve body. We make the decision on the fly to move forward with replacing the valve body with a rebuilt torque converter lockup solenoid from my old valve body.

That brings us to today...the transmission is reassembled, put back in the car, all line pressures are verified and found to be within recommended operating ranges. The car is taken out for a test drive, and you guessed it code P0740 gets thrown again, but it does seem to be shifting much better than before. At this point the shop owner pulls the transmission out for the third time in two weeks.

The torque convertor is being replaced for the second time, and possibly the pump as well. I am attempting to get a new replacement for the broken solenoid, but won't likely have closure on that for several more days.

What on earth are we missing? Any suggestions short of setting something on fire, please let me hear them!

Post by **precopster** » 15 Feb 2016, 22:04

Firstly sorry to hear all this.

TCC lockup is determined and controlled by a spring and piston in the last section (smallest) of the valve body. Perhaps the spring requires replacement. Could it have been missed? If you refer to the Transgo shift kit documentation it shows the location.

badcadman · Post by **badcadman** » 16 Feb 2016, 10:13

Thanks for your comment Mike.

One of the things verified during the rebuild, and replacement of the valve body was if there was a B5 Clutch Control Spring. For my car there is not, and the replacement valve body did not have this spring as well. Documentation that I have read notes that later valve bodies had this spring. I'll get back to you.

Post by **precopster** » 16 Feb 2016, 13:36

Remove the TCM and clean edge contacts thoroughly. You may be fighting a case of edge connector corrosion. Common with this age of car depending on local comditions. You will need a removal tool, a toothbrush and some contact cleaner.

badcadman · Post by **badcadman** » 17 Feb 2016, 21:05

Will be pulling the TCM tomorrow to check for corrosion.

The rebuilt torque converter may be part of the issue... My transmission shop was pressure checking the hydraulic circuit to/from the torque convertor from the valve body and was getting some pressure leakage where there should be none.

As a result, the second new torque converter is now in place. And a new replacement torque convertor lockup solenoid to replace the broken one on the new valve body will be in place tomorrow.

The pump was pulled apart, all clearances in the gerotor assembly were checked and found to be good, and the flatness of the pump cover to the pump housing was checked. There appears to be some warpage in the pump cover in the area of the ports that are heading out to the torque convertor and back, possibly presenting the chance for hydraulic pressure to crosstalk or short circuit the fluid path system.

From the circled areas in the picture it does appear that a significant amount of wear has occurred over the 166,000 miles this car has been through. Thinking back to how the ATF looked when I did the flush at the end of August (looked like the media used in extrude hone; thick, dark and very gritty), I believe this could be a contributing factor. Measures are being taken to flatten the pump cover and get a seal to the pump housing using anaerobic sealant.

Hopefully we are making progress.

Post by **precopster** » 18 Feb 2016, 04:00

Fingers crossed on the diagnosis. Those plates look gnarly!!

badcadman · Post by **badcadman** » 18 Feb 2016, 17:50

A lot of progress has been made. I picked up the car this afternoon after the following was completed: pump cover and pump mating surfaces flattened out and sealed with anaerobic sealer, new torque converter installed and new TCC solenoid installed. From the last few tries at the fix a code would post within a few minutes of driving. There is a slight clunk when going from a low speed coasting condition (less than 15mph) and getting back into the throttle. Other than that it seems back to normal. Overall it seems to be working as I would expect, but I've only put 20 miles or so on it. Will be monitoring closely and reporting back.

Post by **abscate** » 21 Feb 2016, 09:01

Epic gruesome tale, but at least you have shut me up,about complaining about city shifting for a year....

Good luck, hope it's solved

badcadman · Post by **badcadman** » 24 Feb 2016, 19:50

Update after about 200 miles: overall smoothness of shifting is evening out. Upshifts are smooth as are downshifts, and there has only been one 3 to 2 coasting downshift oddity since Thursday. Manual shifting mode is working well, shifts are fairly prompt when called for. No check engine codes have posted.

My advice to anyone who is willing to get this deep into a repair - pull the transmission and inspect the pump thoroughly for proper clearances and wear/warpage on the pump cover. Finish with anaerobic sealant. Bite the bullet and get a reman valve body (or a new one) and you will minimize your messing around.