EMI Interference causing transmission shift issues?

Matthew Owner/Technician Smyrna, Georgia Posted   Latest  
2005 Volkswagen Phaeton V8 4.2L (BGH) 6-spd (09L)
P0735 - Gear 5 Incorrect Ratio
P0729 - Gear 6 Incorrect Ratio

Hello everybody, I've got an interesting one that I haven't had much time to look at other than a test drive and some observations. The core of my post is trying to find a way to test for EMI interference affecting transmission performance on this Phaeton. 

It went to the dealer and of they say it needs a transmission, and while I concede that these transmission have a high failure rate and that is most likely the issue, something about it rubs me wrong. It shift and drives fine except for under high load in higher gears. I've been unable to find any accurate documentation as to how this system works as far as setting the above faults for gear ratio, I assume it's comparing input to output speed?

A little back ground on this, customer bought the vehicle in Florida and drove it back to GA fine, about 2 days later these symptoms started. There is no MIL on for these faults which I thought was odd, The customer is kind of a techy guy (has a bunch of accessories in the car which also may be contributing).

Just wanted to see if anybody has ever ran into an interference situation and if you have developed any way to test for it.

Joe Manager
Houston, Texas


EMI used to measured in the early years with a Bosch 150 MOT(compact motor tester)They have updated them a few times. 

You should be able to pick up any anomalies on the BUS that could be considered static using a high quality oscilloscope on the data lines.

In this case I have scene more often than not that pin fitment, fretting, or corrosion to be the culprit. I have attached a good article on EMI testing.It is a little heavy but you can pick up several theories of operation which will assist in developing a test plan.

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Ryan Manager
St. George, Utah

I am unable to view the attachment, just appears to be a broken image link.

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Joe Manager
Houston, Texas
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Craig Service Advisor
Grand Rapids, Michigan

Man, sounds like reach for good news to me. But hey, I have long arms too. ;) I always admire the effort to avoid condemning the box. You know it happens every day.

You could try looking up the 6Hp19. Data on these can be a royal pain, and it's been awhile since I've had the pleasure. Our diagnosis process for a persistent hard shift with codes like this would go something like this.

1.) Check fluid level and condition. I know it seems obvious, but it goes without saying, this is key info, and you'd feel silly over-complicating things if the answer was here all along. If the fluid is highly metallized, you'd be working in vain to try and find good news for a bad news situation, might as well rule it out. You don't need a big sample at all (really the spill from a level check is often enough).

2.) If this is load sensitive, it screams of a hydraulic valve body issue. We vacuum tested a LOT of valve bodies (all makes and models) to verify some of these issues. This is unnecessary if you find a lot of debris, naturally.

The problem: Cost of VB repairs, combined with high probability of other subsequent failures, and the liability for the subsequent failures being placed on the "last one to touch it". I've seen a lot of folks swear off Euro cars after buying a used one and being faced with this dilemma.

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Danny Technician
Cleveland, Tennessee

Take a look at your speed sensor data p1735 is a speed sensor code

That will cause it to act up causing ratio codes 

Aalternator ripple comes to mind on emi 

Good luck 

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