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Matt, Engineer
Category: Audi
Satisfied Customers: 21610
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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Audi A4: Hi i just got used 2003 audi a4 1.8t. The seller ripped

Customer Question

Hi i just got used 2003 audi a4 1.8t. The seller ripped me off. I took the car to mechanic he told me that car has 13 problems. Here's the list.

13 Faults Found:

16804 - Catalyst System; Bank 1
P0420 - 002 - Efficiency Below Threshold - MIL ON
18062 - Please check DTC Memory of Instrument Cluster
P1654 - 004 -
17544 - Fuel Trim: Bank 1 (Add)
P1136 - 001 - System too Lean - Intermittent
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 008 - - Intermittent
16685 - Cylinder 1
P0301 - 008 - Misfire Detected - Intermittent
16688 - Cylinder 4
P0304 - 008 - Misfire Detected - Intermittent
18339 - Coolant Fan Control Module (J293)
P1931 - 004 - Malfunction - Intermittent
17887 - Brake Boost Vacuum System
P1479 - 008 - Mechanical Failure - Intermittent
18613 - Performance Malfunction in Cooling System
P2181 - 008 - - MIL ON
17887 - Brake Boost Vacuum System
P1479 - 008 - Mechanical Failure - Intermittent
18068 - Coolant Fan Control 1
P1660 - 002 - Short to Ground - Intermittent
16686 - Cylinder 2
P0302 - 008 - Misfire Detected - Intermittent
17658 - Fuel Level too Low
P1250 - 008 -
Please help me out.
Submitted: 4 years ago.
Category: Audi
Expert:  Matt replied 4 years ago.

well at least 5 of those are probably down to one cause as if you have a faulty O2 sensor in the exhaust then then can lean things out and give misfires as the codes indicate

so 1st check for exhaust leaks before the O2 sensor as the sensor will see any extra air pulled in as fresh / lean fuelling and be adding fuel to compensate.

so despite it thinking its lean its actually running rich

this can lead to catalyst failure as the extra fuel can re-light inside and melt the catalyst

The best way to find an exhaust leak is to run the engine from cold and feel around the exhaust joints with your bare hands - you'll have about 30 seconds before it all gets too hot and you should feel any escaping gas blowing over your fingers

If this look s OK I'd consider replacing the O2 sensor

also these cars are prone to issues with the ignition coils so that the other possibility that cyls 1,2 & 4 need a new coil each if you move the no.3 coil to one of the misfiring cylinders and the fault moves with it then you know that the coils do need replacing

Some of these faults could also be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.

As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.

if the engine condition is the same then chances are the meter or the connection to it is faulty

Air leaks are very temperature dependent as gaps can open or close up as things expand with heat, so the weather and engine temperature can effect them.

This leads them to be quite intermittent in the case of mild leaks

its also worth cleaning the airflow meter by removing it from the car and spraying the exposed sensor wires inside the tube with a brake or switch cleaner - ensure that the cleaner is one of the old fashioned, non Eco type that does not leave a residue

On no account touch the sensor wires with anything physical as they are extremely fragile


Customer: replied 4 years ago.

sorry i forgot to mention couple of things.... my temperature gauge is at low, RMP fluctuates when i start car like goes to 3000-4000 then drops to 500 and then up again for 7-8 sec. RPM also goes down after 30 mins of driving when i apply brakes and some times car shuts too. Passenger side fan is not working and one purple wire coming out of fan/coolant module is sliced. Oil light is comes and goes and car burning way too much of gas. One more thing car has custom exhaust.


Expert:  Matt replied 4 years ago.

this is starting to sound like too many faults for them all to be true

so I'd suspect that there may be an issue with battery voltage or a short somewhere in the loom

So check that the main battery connections are tight and in good condition also check the earth strap to the engine / gearbox. Next I'd check the current drain aspect, the best way to find what circuit ( if any) is causing the excessive currant drain is to fit a current sensing multimeter in series with the positive battery lead on the car and the battery, or use a current clamp meter on the battery positive cable. A typical current drain with everything off and un-alarmed should be around 0.05Amp and if its higher than this remove a fuse and re-measure, if measurement doesn't change then replace the fuse and remove the next.

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