Can P0638 fault be caused by low voltage?

On the way home on the highway tonight, my JSW motor felt like it cut out for a couple of seconds, came back on, then cut out completely. Glow plug and workshop lights came on. I coasted over to the shoulder and found that the motor was bucking, like a carbureted car that's running out of gas. I chugged down the shoulder for a couple of hundred feet and then it suddenly smoothed out and I was able to drive home normally. I ran a VCDS scan and found the results below.

My question is: the voltage shows 10.64V - shouldn't it be the normal operating voltage of around 13 or whatever? And it if is indeed low, is it likely that problem is caused by low voltage, and that the throttle control valve module signal that the code implicates is really a symptom rather than the cause?

001592 - Throttle Body Actuator Bank 1 (J338): Implausible Signal
P0638 - 000 - - - Intermittent
Freeze Frame:
Fault Status: 00100000
Fault Priority: 2
Fault Frequency: 2
Mileage: 142424 km
Time Indication: 0
Date: 2000.00.00
Time: 05:15:20

Freeze Frame:
RPM: 4347 /min
Speed: 93.0 km/h
Voltage: 10.64 V
Lambda: 99.4 %
Bin. Bits: 00000000

I'm not thinking the low voltage is the cause. Recheck the voltage with your VSDS. Do you get similar readings?

You have an intermittent problem and can be tough to figure out for certain.

~ Check the connection at the throttle body. Is it aircraft engine quality clean? No possible issues, like new.

~ Inspect the wiring loom back to the Motronic ecu. Similar quality level.

~ Take ohm readings on the throttle body. Are they in specification? (I don't have the ohm spec. Perhaps in Bentley? or another member? or compare with a new one)

You could wait till it happens again, it might be a long time or next time you take it out.

I have seen Motronic connected devices that ohm out perfectly, but still have a fault code that is corrected by a replacement device.

Thanks, Sutgart - I checked the connector this morning and it was shiny clean inside. I shot some electrical cleaner into it anyway. Then I had to jump it and it was still extremely hard to start, and when it finally did start it's running rough again. I'm just gonna tow it in to the dealer... I might as well use my extended warranty.

You need to try to charge the battery and replace it if it won't take a charge.

Bill

Sound like you need a battery. Just replace the battery on my 09. These ECM are very picky about the voltage.

The verdict is: a bad Mechatronics unit was causing the anti-theft system to kick in and disable the car. They replaced it at no charge under the 100K mile DSG warranty. I'm picking it after work today.

Meh. Motor shut down for a few seconds on the highway this morning, same as before. Back in the shop.

Glad you have an extended warranty.

Stutgart said:

Glad you have an extended warranty.

Click to expand...

Yeah, unfortunately it isn't helping much since they can't figure out the problem. No codes stored, wiring harness looks OK, it runs wonderfully when they drive it. This morning on the way in the TPMS light came on... they said the controller was bad and reflashed it. I can't imagine that that's just coincidence. The mechanic thinks that the original code was caused by the low voltage showing in the Freeze Frame, but has no idea why that happened since everything now is hunky-dory. Turning out to be a real bugger.

I got to thinking that one reason the warning lights would come for a few seconds on but no codes stored would be if the power cycled, which makes me suspect the ignition switch or power supply relay. Does this model have a relay 109/J329 equivalent? I see lots of references to J329s through 2005 or 2006 models in the forum, but so far have only found one mention of a power supply relay for 2009 but the poster didn't include a part number.

Just to close this out - the dealer was finally able to reproduce the condition and replaced the J519 unit and a relay which they said was fried by a power surge from the failed J519. The relay has the same part # as the 2005-2006 Power Supply Relay 460/J329 that I mentioned in my previous post. So it seems a good bet that this model does indeed suffer from a similar condition to the earlier ones.

I was going to drop this out of apathy, but got to thinking that I'd feel bad if someone used my experience to diagnose a similar issue. It appears that the J519 module and relay 406 were casualties, not the root cause. It stalled and refused to restart at a stop sign. Same symptoms: GP and MIL flashing, motor chugging but won't move forward (I was on an upgrade), then stalled; when I tried to restart it, it cranked a bit slowly and then made a screeee sound like the starter disengaging from the flywheel while it was still trying to crank. Got the guy behind me to back up so I could push it back out of the road & after sitting for 5 minutes or so I got it restarted and limped back home with the motor cutting in and out. I could hear a relay clicking under the left side of the dash but because of the underdash covered I couldn't feel around to see which relay it was. By the time I got home it was running normally again. I towed it back to the shop on my dime and of course it's starting and running perfectly for them.

BTW to those who earlier suggested the battery - that was the dealer's initial diagnosis at the first visit too, so I picked the battery up from them & had it tested and it checked out fine. When they put the battery back in it started right up. This battery is a year or two old, and when the previous one went bad the only issue it caused was slow/no cranking - once I got the car started it ran fine. So, the battery is the first thing we ruled out.

Glad you got this solved. Did the extended warranty cover this?

My whole point is that it isn't solved , and that I'd feel bad if someone down the road needlessly replaced some expensive parts based on my post. The car is back with the dealer now with them once again unable to reproduce or diagnose the stalling. I told them to keep it as long as they need it and the warranty covers it.

So far the extended warranty has covered $1K+ for the J519 module, the 406 relay, the TPMS sensor, and the labor for diagnosis and R&R. The Mechatronics replacement was free under VW's extended DSG warranty. I'm out of pocket $100 for the extended warranty deductible, and I've used two out of my three prepaid AAA tows for the year.

But as of now the ticket is still open...

curovo said:

My whole point is that it isn't solved , and that I'd feel bad if someone down the road needlessly replaced some expensive parts based on my post.

Click to expand...

I wouldn't worry about that. I sure would hope that anyone would take the time to read the entire thread before purchasing parts based off of a forum thread.

...should have read your post more carefully.
Hope they can solve your issues.