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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. |
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 |
great tip on the TCU software screwup
I think you nailed it, johnnya.
Originally Posted by johnnya
(Post 25217054)
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. 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. |
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. |
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. |
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. |
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. |
There are replacement parts available for the connector:
3A0973204 |
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.
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
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.)
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).
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. |
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