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Audi A4 (So many check engine codes....I don't know what to do!)

I have a 2000 A4 quattro Avant with approx 118K mi. I have been getting the P1136, Long term fuel trim…too lean code on and off for a couple of months. Engine is idling a little rough, MPG is down slightly, sometimes a black carbon looking smoke in exhaust at idle.

I have had both the MAF sensor and turbo recirc. valve replaced at the “advice” of the dealer. The code still was appearing until I picked it up from the shop yet again and noticed that the light came on approx 5 seconds after startup, much quicker than it normally takes once reset, (the shop had reset it).

I put my scan tool on it and I am no longer getting P1136 (lean mix) but 10 different codes all pertaining to O2 sensors, sec air sys, turbo valves, etc…and a lot of short to ground codes.

Could a faulty O2 sensor cause all these codes (see below)?

I have just replaced the upstream O2 sensor, reset the codes and still getting the error codes. Could there be some sort of a system relay bad? or could a faulty downstream O2 sensor cause these codes? I have looked for shorted wires, loose connectors, etc. but found nothing. I am at my wits end with this one and any help will be appreciated.

P1425 Tank Vent. Valve short to ground

P1117 O2 sensor heater circ, bank 1 sensor 2 short to ground

P1435 Sec. air inj sys pump relay circ short to ground

P1421 Sec air inj sys valve circ short to ground

P1289 Turbo bypass valve short to ground

P1473 EVAP Emis cont LDR circ, open circ

P0102 Mass or Volume Air Flow a Circ low

P1115 O2 sensor heater circ, bank 1 sensor 1 short to ground

P1114 Bank 1, sensor 2 Internal resistance too high

P0140 O2 sensor circ no activity detected, bank 1, sensor 2.

A dead computer can make all of this and more, so it should be put on the list of suspects.

I’m not an expert, but this looks like a random collection of errors, not the result of a mechanical failure in the engine. More likely a computer/wiring problem than an engine problem?

Look for loose or unconnected plugs/sockets in the wiring harness or a damaged wiring harness. Maybe low or erratic battery voltage? Hope it is not the computer.

If all those codes showed up after you installed the new O2 sensor then I suggest you disconnect the O2 sensor and then see what happens. If they clear up then something isn’t connecting correctly to the new O2 sensor. If the codes are still showing up then check for a possible problem in the wiring that may be due to your work on the car. Make sure that the wiring hasn’t touched the exhaust system somewhere and damaged the wires. Also look for a bad cable connection, but since there are a lot of short to ground warnings it sounds like the wiring has been damaged somewhere if the O2 sensor isn’t causing the trouble.

The short to ground warnings showed up before I installed the new O2 sensor. They didn’t show up until the lean fuel mix error magically disappeared after being there off and on for a few months. However they did show up after being in the garage to repair the washer fluid pump. I have looked for disconnected wiring, bare wiring, etc and see nothing but I will look a little harder. Thanks for the advice.

The trim/lean code most likely can’t happen due to the other code troubles.

Another thing to check is fuse 34 in the fuse panel. It supplies power to some of those sensors at least.

a bad maf meter will ruin o2 sensors

Go over to

Much better chance of getting useful info

OK…well you are the big winner for this round. Pulled fuse 34 and it was blown. Replaced fuse, reset codes and they haven’t shown back up within the time that they normally did. I am still going to look around for anything that may have caused it to blow. I really appreciate the help!!

You found fuse #34 blown, replaced it, and all (now) is light and happiness; but, the shorts will be back unless they were caused by the repairers.
If the shorts do come back, you could use a short circuit tester, like this one, to find the shorts:

Why do consumers put up with nonsense like this??

Well…everything good til I ran it to work this morning and when I shut off the car and turn it back on the check engine lights is back and fuse #34 is blown again. Do you have any idea what all components are on that circuit? I guess I will just start eliminating each component at a time to try and find this booger.

Did somebody say the wiring diagram would reveal what parts feed off fuse #34?

no, but that is what I am wondering if anyone has. A detailed list of components fed from fuse #34.

The first place I suggest you look for the intermittent trouble is near the O2 sensor. Make sure that the sensor wiring hasn’t come in contact with the exhaust system and burned the insulation on the wiring. Also check out the MAF area along with the turbo area for any wire problems. Especially look for damage to the wiring caused by touching a hot surface or a pinched wire.

This is from a “power distribution” wiring diagram. It’s available, to you, through your public library Web site access to ARRC. On your public library Web site, go to: Electronic Databases > Reference > input your library card number at Auto Repair Reference Center > Wiring Diagrams > Power Distribution.
Fuse #34 supplies power to:
exhaust temperature sensor;
EVAP canister purge regulator valve;
leak detection pump (A4);
camshaft adjustment valves;
Mass Air Flow sensor;
secondary air injection solenoid valve;
oxygen sensors,
idle air cutoff valve;
secondary air injection relay;
waste gate bypass regulator valve;
intake manifold change over valve.
That’s all.
Examine the wiring all over the engine. Look for frayed wiring, burns, breaks, pinches, sharp corners, etc.

It sounds like the “fuse 34” and the circuit it protects may have been the problem, based on the postings, and kudos to Cougar for apparently nailing this one. If the “too lean” code keeps recurring, keep in mind that while the computer thinks the engine is running lean, it probably isn’t. The computer is probably confused by incorrect or conflicting sensor data and is attempting to correct a problem that may not exist. When the computer tries to correct what it thinks is a lean condition, based on data gathered from its sensors, which may not be working properly, it adds more fuel. This can make your mileage go down and cause black smoke from the exhaust, classic signs that the engine is actually running too rich—because the computer is making it run too rich, attempting to erroneously correct what it thinks is a lean condition (which may not even exist) by dumping more fuel in. I’m not sure what your actual problem is, but I wanted to attempt to explain that while the computer’s diagnostics are useful, they’re certainly not infallible. A mechanic that’s a good diagnostician will take this into account and see the forest for the trees. Lesser ones will throw parts at the problem without understanding the situation.

The engine ran fine until you restarted it, right? Was the engine cold, or had you just shut the engine off?
What happens, electrically, when you just turn the engine on, that’s an extra electrical load on that power supply (fuse #34)? The oxygen sensor heaters are turned on, is what. One of those oxygen sensor heater wires may be shorted to ground, or, to another wire.
There are other actuators (valves) which get turned on later as the engine heats up, or, some other condition is met, for a monitor to be run.
The EVAP canister purge control valve isn’t on constantly; nor, are 3 or 4 other valves. It’s possible, not likely, for a component to be shorted internally.

Thanks to everyone who replied to my post. I will be away for a few days until I get to work on the car again, but I will let everyone know what I find so if anyone else runs into this, maybe it will help. Again thanks to all.

You are welcome for the help. Please continue on with any new posts here so all the postings will be in one thread. It makes things easier for all involved.