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All PRND432 lit, tcu incorrectly coded, mass air flow, and abs codes

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All PRND432 lit, tcu incorrectly coded, mass air flow, and abs codes

Old 09-28-2018, 10:01 AM
  #1  
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Default All PRND432 lit, tcu incorrectly coded, mass air flow, and abs codes

1997 Audi A8Q, ABZ.

I rebuilt the trans myself after having the usual blown A drum when I got the car. Been driving it regularly since the Spring. Because of this, I don't think the fluid is dirty. A very slight drip from the front of the trans somewhere makes me top it off every couple of months. It doesn't usually take much.

A couple days ago I noticed all trans gear indicators PRND432 lit up, and check engine light on. It seems to run just fine. I know what limp mode feels like. Got home, autoscan showed a whole boatload of faults:

Engine
8 Faults Found:

16705 - Engine Speed Sensor (G28)
P0321 - 35-10 - Implausible Signal - Intermittent

17968 - Maximum Engine Speed Exceeded: Engine Warranty VOID!
P1560 - 35-10 - -) - Intermittent

17604 - Oxygen (Lambda) Sensor Heater Circuit: B1 S1
P1196 - 35-00 - Electrical Malfunction

17605 - Oxygen (Lambda) Sensor Heater Circuit: B2 S1
P1197 - 35-00 - Electrical Malfunction

16486 - Mass Air Flow Sensor (G70)
P0102 - 35-00 - Signal too Low

16518 - Oxygen (Lambda) Sensor B1 S1
P0134 - 35-10 - No Activity - Intermittent

16538 - Oxygen (Lambda) Sensor B2 S1
P0154 - 35-10 - No Activity - Intermittent

16541 - Oxygen (Lambda) Sensor B2 S2
P0157 - 35-10 - Signal too Low - Intermittent
-------------------------------------------------------------------------------
ABS Brakes
1 Fault Found:
00283 - ABS Wheel Speed Sensor; Front Left (G47)
30-10 - Open or Short to Plus - Intermittent
-------------------------------------------------------------------------------
Airbags
4 Faults Found:
01216 - Seat Occupant Sensor; Passenger Side Rear (G178)
32-10 - Resistance Too High - Intermittent

01219 - Rear Side Airbag Igniter; Driver Side (N201)
32-10 - Resistance Too High - Intermittent

01220 - Rear Side Airbag Igniter; Passenger Side (N202)
32-10 - Resistance Too High - Intermittent

01215 - Seat Occupant Sensor; Driver Side Rear (G177)
32-10 - Resistance Too High - Intermittent
-------------------------------------------------------------------------------
Centr. Locks
1 Fault Found:
01371 - Alarm triggered by Door Contact Switch; Driver's Side
35-00 - -
-------------------------------------------------------------------------------
Auto Trans
1 Fault Found:
18157 - Transmission Control Unit Incorrectly Coded
P1749 - 35-00 -

I don't know how old some of these are, so I cleared the codes. Ran autoscan again right away to prove codes were cleared. Checked ECU/TCU box under hood; bone dry, no signs of past or present water in it. Upon restarting car, all PRND432 lit again, almost immediately. Shut off and restarted, now check engine light on as well. Autoscan run again; only 3 codes now:

Engine
1 Fault Found:
16486 - Mass Air Flow Sensor (G70)
P0102 - 35-00 - Signal too Low
-------------------------------------------------------------------------------
ABS Brakes
1 Fault Found:
00283 - ABS Wheel Speed Sensor; Front Left (G47)
30-10 - Open or Short to Plus - Intermittent
-------------------------------------------------------------------------------
Auto Trans
1 Fault Found:
18157 - Transmission Control Unit Incorrectly Coded
P1749 - 35-00 -

The Bentley manual says the trans fault should not light the check engine bulb.

Drove to work and home yesterday, about 50 miles; still seems to be running fine.

Autoscan run again, showing the same 3 codes, plus some O2 sensor codes (again):

Engine
6 Faults Found:
16486 - Mass Air Flow Sensor (G70)
P0102 - 35-00 - Signal too Low

16538 - Oxygen (Lambda) Sensor B2 S1
P0154 - 35-10 - No Activity - Intermittent

17604 - Oxygen (Lambda) Sensor Heater Circuit: B1 S1
P1196 - 35-00 - Electrical Malfunction

17605 - Oxygen (Lambda) Sensor Heater Circuit: B2 S1
P1197 - 35-00 - Electrical Malfunction

16541 - Oxygen (Lambda) Sensor B2 S2
P0157 - 35-10 - Signal too Low - Intermittent

16518 - Oxygen (Lambda) Sensor B1 S1
P0134 - 35-10 - No Activity - Intermittent
-------------------------------------------------------------------------------

ABS Brakes
1 Fault Found:
00283 - ABS Wheel Speed Sensor; Front Left (G47)
30-10 - Open or Short to Plus - Intermittent
-------------------------------------------------------------------------------
Auto Trans
1 Fault Found:
18157 - Transmission Control Unit Incorrectly Coded
P1749 - 35-00 -

Started the car and checked some engine groups to see mass air flow while idling; seems to be in spec (about 6 g/sec; Bentley says it should be 3.9 to 6.5 g/sec), except 3 groups had the words mass flow, but only 1 read anything live:

Address 01: Engine (4D0 907 557 D)
18:05:27 Group 002
760 /min RPM
21.4 % Load
5.97 g/s Mass Flow
8.3 BTDC Ign. Timing

18:05:27 Group 005
770 /min RPM
760 /min RPM
-0.15 g/s Mass Flow
0 0 0 Bin. Bits

18:05:27 Group 006
760 /min RPM
-0.15 g/s Mass Flow
0.29 g/s Mass Flow
0 0 0 Bin. Bits

I had all 3 groups up on the screen at the same time.

Why are there multiple mass flow indications in the different groups, with some dead? The live one was moving around just slightly, as I'd expect.

TCU incorrectly coded? Huh? They can't just decode themselves, can they?

I saw a thread claiming that changing out a mass flow sensor solved the PRND432 lit up; https://www.audiworld.com/forums/a8-...coded-2775283/. I saw another that said the ABS was tied into the TCU in some manner; I have had intermittent ABS and brake warning lights come on over the past several months, but shutting off and restarting the car always turns them off.

With all these codes suddenly appearing all at once, I'm wondering if I had something snag a wiring harness while driving and loosen or cut it. Would all these wires be in the same bundle? (A pair of the O2 sensor cables go up through the floor into the cabin, one on each side.) Also, it's rained heavily in the last couple of days. I haven't put the vehicle on a lift yet to check underneath.

Any comments are welcome. Thanks.
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Old 09-28-2018, 01:10 PM
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Actually, 18157 - Transmission Control Unit Incorrectly Coded
likely only means that the load signal is missing due to the mass flow sensor error.

There is a software bug documented in the PDF files from erwin.audi.com:

For gearbox control units with software version "D26", "D29" and "D32"
the fault codes "18157 / P1748" and "18265 / P1857" are interchanged.


I had the transmission go into limp mode regularly because a faulty mass flow sensor always caused
16487 – Mass Air Flow Sensor (G70): Signal too High
and the load signal was no longer available.

This description was very helpful for me:
98 A8 D2 MAF (Mass Air Flow) Problems ? Audi
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Old 09-29-2018, 06:00 PM
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Default great tip on the TCU software screwup

I think you nailed it, johnnya.
Originally Posted by johnnya View Post
Actually, 18157 - Transmission Control Unit Incorrectly Coded
likely only means that the load signal is missing due to the mass flow sensor error.

There is a software bug documented in the PDF files from erwin.audi.com:

For gearbox control units with software version "D26", "D29" and "D32"
the fault codes "18157 / P1748" and "18265 / P1857" are interchanged.
Thanks for bringing my attention to the software bug. Without knowing about it , I'd have been hunting around the Trans Control Unit ("incorrectly coded") instead of the engine. It's in my Bentley as well, but there might be a misprint in the documentation - it says 18157/P1748, not 18157/P1749. Nonetheless, the error, if one goes to and reads about 18265/P1857 instead, is about "signal for the actual engine torque". This is probably the same as what you refer to as "load signal". So that suggests to me that it's not a separate "trans coding" fault, but another Mass Air Flow fault, as you suggest.

So then, chasing mass flow sensor, I found a dead power supply wire to the mass air flow sensor. Blown fuse. (Don't know why I saw what looked like a live signal earlier. Hmmm. Same fuse that supplies the O2 sensor heaters, likely explaining those codes as well.

Replaced the fuse, no errors right off the bat (last time it tripped immediately after startup). Drove it around the block, and halfway around, got a check engine light. At home, got the code for oxygen sensor no activity, front sensor left side (bank 2, sensor 1). No blown fuse, though. Fished up the O2 sensor cable from under the hood, and Bingo! found it had melted against the exhaust, and made a mess of the wires. That probably blew the fuse before. Only the harness side is melted.

Some quick looking tonight finds no harness side connector available from rock auto and a few other places (so far). I'll keep looking, but I might just solder the wires together (after twisting and running first to check functionality). Some replacement O2 sensors give you a replacement harness side connector (different than original) anyway, with which you need to replace the original (in my case melted) connector.

Maybe that same fuse took out some other stuff that was flagged as well. I'll update as I get more info.

Thanks.
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Old 09-29-2018, 10:45 PM
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Don't solder the cables. Apparently the sensors have to be able to "breathe" air through the wires to work properly.

I exchanged both O2 sensors on my 1997 ABZ with BOSCH 0 258 003 842. The old OEM ones were are also made by BOSCH.
These replacements just have a longer cable that needs to be fixed at the connector holder with cable ties.

They were pretty affordable (in Germany the Audi branded ones are 5 times more expensive):
https://www.motointegrator.de/artike...-0-258-003-842

To exchange them, I used similar tools as shown in this thread:
https://forums.quattroworld.com/a8/msgs/49929.phtml
Both sensors could be reached from the top after temporarily removing the plastic connector holders. I did not remove the wheel.
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Old 09-30-2018, 05:22 AM
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hillpc,

If you want plug-an-play O2 sensors order the BECK/ARNLEY 1564176 from RockAuto. The plug is an exact match to the OE on your Audi so no splicing needed. See in my signature below Oxygen Sensors for my write up on replacing both my front and rear O2 sensors.

Good luck.

Last edited by 2001 S8; 09-30-2018 at 05:31 AM.
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Old 09-30-2018, 08:51 AM
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Please be aware that the O2 sensors on a 1997 ABZ are not the same as on the 2001 facelift model.

The BOSCH 0258003842 for the 1997 ABZ do actually have the correct Audi plug (with the Audi symbol grinded away) and are built by the OEM. For sensors, I would not recommend using non-OEM aftermarket brands.

Last edited by johnnya; 09-30-2018 at 08:54 AM.
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Old 09-30-2018, 11:41 AM
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All OEM-style plugs on O2 sensors are likely out of play, since my harness-side connector is destroyed (melted), with broken wires as well. I haven't found a replacement available, though I suppose I could start hunting through junkyards. I am trying to salvage it, though, by chopping more and more of the melted plastic off it. The locking function won't work anymore, at the very least. I plan to have the sensor back in operation today.

Regarding soldering, it seems that the sensor (not heater) wire(s) serve as an air conduit to some part of the sensor. I don't think this means that soldering anywhere along their length destroys this functionality. As long as air can get to the wire strands before the sensor, I'd think it would still work, though I can't speak to how much wire has to be exposed. Where does the air get in now, at the connector? I will crimp the sensor wires in my repair attempt.

Last edited by hillpc; 09-30-2018 at 11:52 AM.
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Old 09-30-2018, 12:14 PM
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There are replacement parts available for the connector:
3A0973204
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Old 10-03-2018, 07:13 AM
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Default Likely summary of events for bogus 18157/P1749 code - TCU Incorrectly Coded

The problem seems to be solved. Here’s my summary of how I think it went down.
  • Unbeknownst to me, left pre-cat O2 sensor G108 connector lying against the exhaust pipe, melts through, shorts O2 sensor heater power lead to ground and blows fuse ST4 S3, which supplies mass air flow sensor G70 and 2 pre-cat O2 sensors G39 and G108 heaters Z19 and Z28.
  • The dead mass air flow and pre-cat O2 sensors throw several codes and activate the check engine light:
16486 - Mass Air Flow Sensor (G70)
P0102 - 35-00 - Signal too Low

17604 - Oxygen (Lambda) Sensor Heater Circuit: B1 S1
P1196 - 35-00 - Electrical Malfunction

17605 - Oxygen (Lambda) Sensor Heater Circuit: B2 S1
P1197 - 35-00 - Electrical Malfunction
  • The ECU and/or TCU (they communicate for this purpose) can’t get an engine torque signal from MAF sensor, TCU throws incorrect code 18157/P1749, due to bug in TCU software (Bentley version of bug notification): The fault codes 18157 / P1748 and 18265 / P1857 were interchanged by mistake on transmission control units with data versions D26, D29 and D32.
  • 18265/P1857 is a problem with the load signal. I believe I must have software version D26:
Address 02: Auto Trans Labels: 01L-927-156.lbl
Part No: 4D0 927 156 K
Component: AG5 01L 4.2l4V RDW D26
Coding: 00011

All PRND432 lit. (Not a true limp mode as usually seen, when only 5th gear or reverse are available. Seems to run fine to me, maybe torque converter lockup not there, since the tach may look like it’s running a little high on the highway.)
  • Replaced the fuse. At this point I had not yet found the melted O2 sensor connector.
  • Drove it around the block, did not blow fuse, but left front O2 sensor signal dead or shorted, throwing 1 engine code and activating check engine light:
Address 01: Engine Labels: Redir Fail!
Part No: 4D0 907 557 D
Component: 4.2L V8/4V MOTR AT D03
Coding: 01273
1 Fault Found:
16538 - Oxygen (Lambda) Sensor B2 S1
P0154 - 35-00 - No Activity

This makes sense to me because I have before had intermittent faults from a wire melted against the exhaust (engine rpm signal; same general location. Self-inflicted by not tying off cables better after trans rebuild!). The right kind of random movement while driving makes or breaks the offending contact(s).
  • Found the melted O2 sensor connector, cut away all the melted parts and spliced in new wiring, crimping the signal wires and soldering the heater wires. Taped up. Problem solved.
  • The only remaining fault,
00283 - ABS Wheel Speed Sensor; Front Left (G47)
30-10 - Open or Short to Plus - Intermittent

must be unrelated.

johnnya broke the case open with his lead on the code-reporting software bug. Thanks.

Last edited by hillpc; 10-03-2018 at 07:30 AM.
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