
The Hobby Car
2003 VW Passat GLX 4motion Wagon
This is my Passat. Looks great but doesn't run. Hence has become a project now. While the previous owner seems to have kept it pretty well with regular maintenance, but the car misfires. The reason needs to be determined. I have a list of the problems that I see for now, and the tests I do to go about diagnosing it.
Problems
Fixed
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Oil leakage on the Bank 2 valve cover
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Misfire on bank 2: Cyl 4,5,6 diagnosis
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Bank 1 O2 sensor downstream
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Rocking front axle
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Vacuum Leak
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Foggy headlamps
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Ignition cut off on the Drive gear.
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Transmission oil temperature too high.
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Transmission range sensor fault
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Exhaust leak
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Auxiliary fan replacement
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Fog lamp replacement
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Axle flange leak
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Coolant leak
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Timing belt replacement
Error Codes
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P0300 – Generic Misfire
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P0304 – Cylinder 4 misfire
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P0305 – Cylinder 5 misfire
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P0306 – Cylinder 6 misfire
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P0141 – O2 Heater Circuit (Bank 1 Sensor 2)
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P0711 - Transmission Fluid Temp Sensor (G93)
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P0706 - Transmission Range Sensor (F125)
Diagnostics & Service
1. PCV System

PCV or positive crankcase ventilation system clears residual fuel vapours that may have seeped into the crankcase through the oil/compression rings at the piston. The PCV system ensures that no excess pressure is built up in the crankcase due to these vapours. The excess pressure can cause the oil to leak from the valve covers. Replacing the PCV valve fixed the oil leak from the sides.
Problems
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Oil leakage on the Bank 2 valve cover
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Misfire on bank 2: Cyl 4,5,6
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Bank 1 O2 sensor
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Rocking front axle
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Spark Plug wires broken on connectors at coil
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Vacuum Leak
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Foggy headlamps
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Ignition cut off when gear changed into Drive.
Error Codes
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P0300 – Generic Misfire
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P0304 – Cylinder 4 misfire
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P0305 – Cylinder 5 misfire
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P0306 – Cylinder 6 misfire
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P0141 – O2 Heater Circuit (Bank 1 Sensor 2)
2. Vacuum System

I couldn’t identify any broken vacuum line or open line to find the leak. However, old vacuum lines were plastic and became brittle overtime. Could easily brake. Replaced them with new vacuum lines that are more flexible and easier to work with. Checked Vacuum pressure at the end at each end of each connection. Seemed to be holding just fine.
Problems
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Oil leakage on the Bank 2 valve cover
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Misfire on bank 2: Cyl 4,5,6
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Bank 1 O2 sensor
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Rocking front axle
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Spark Plug wires broken on connectors at coil
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Vacuum Leak
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Foggy headlamps
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Ignition cut off when gear changed into Drive.
Error Codes
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P0300 – Generic Misfire
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P0304 – Cylinder 4 misfire
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P0305 – Cylinder 5 misfire
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P0306 – Cylinder 6 misfire
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P0141 – O2 Heater Circuit (Bank 1 Sensor 2)
3. Foggy Headlamps

This is an easy fix hence I did it quite in the early stages. It was a 4 step process with an online available DIY kit
Problems
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Oil leakage on the Bank 2 valve cover
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Misfire on bank 2: Cyl 4,5,6
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Bank 1 O2 sensor
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Rocking front axle
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Spark Plug wires broken on connectors at coil
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Vacuum Leak
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Foggy headlamps
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Ignition cut off when gear changed into Drive.
Error Codes
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P0300 – Generic Misfire
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P0304 – Cylinder 4 misfire
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P0305 – Cylinder 5 misfire
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P0306 – Cylinder 6 misfire
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P0141 – O2 Heater Circuit (Bank 1 Sensor 2)
There can be a whole bunch of reasons for misfires. From here onwards I try to go with all the checks that you would for a misfire diagnosis. Critical observations here are that the misfire Exists in all cylinders of one bank. That is a good starting point, but while I can, I check all the components as I go.
4. Spark Plugs
Physical Inspection

Visual
In the visual inspection I am looking for the gap between the center electrode and the grounding electrode (aka electrode gap) which seems to be perfectly fine. I am also looking for any signs of oil / fuel breaching and the color in general of the plugs. I am also looking for any settlement / burn marks around the center electrode to indicate the health of the combustion.​
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Smell
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Smell test is a little tricky but combined with the visual test for any burn marks/ settlement can he helpful. I got a strong smell of unburnt fuel which could indicate the rich mixture before burning or the spark plug inadequately or only intermittently igniting the mixture.
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Spark Test

In this test, I pulled out the spark plug and disconnected the corresponding injector to avoid unnecessary fuel. I grounded the grounding terminal of the spark plug and cranked the engine. I repeated the exercise with each cylinder. I found that all the spark plugs were igniting just fine.
5. Cylinder Compression

It is also possible that there is damage to the cylinders, and they are not holding pressure which is why the rpm won’t rise above 3000. The compression tool is plugged into the spark plug thread and the engine is cranked for a few seconds. The pressure should be around 190 psi and should be consistent throughout the cylinders. This seems to be the case, which would imply that the engine in fact is good.
6. O2 Sensor Swap
The error on the OBD tool indicated that Bank 1 Sensor 2. The downstream sensors exist only for emission reporting and do not have any role in controls. However just for the sake of covering all bases, I swapped out the O2 sensor to see if the error persists. I swapped out the O2 sensor without plugging it in, essentially simulating perfect air. It seemed like after plugging in the sensor, the error for the O2 sensor went away, however the engine did not run any better.
7. Wiring Harness
The whole of bank 2 misfiring can also indicate the error with the harness going to the bank 2. To check if the electrical wiring is okay, I did a continuity check by connecting the positive of the voltmeter to the wire injector connector and the negative to the ground (vehicle chassis). The wires seem to be continuous and hence this is not the problem.
8. Spark Plug Wires
Wires:
Spark plug wires can also be a source of shorting near the metal body of the engine. This can be due to worn out insulation. This can be checked via spraying some water at the wires and looking for any sparks. The vehicle passes this test as well. This indicates that insulation of the wires is not the problem.

Connectors:
The next test is to visually inspect the wires at the connector ends. After plugging the wires from the coil pack, it was noticed that the wires were broken from the edges. This could cause a loose connection during vehicle operation causing intermittent missing. It might be worth replacing these wires.
9. Fuel System
To check the misfire and the ignition cut off for drive gear I checked is the fuel system. There are 2 things that could be going wrong.
Fuel Pressure Check:

Insufficient fuel pressure can be due to a problem with the fuel pump or a clogged fuel filter. I replaced the fuel filter and checked the fuel pressure with a pressure fuel pressure gauge. Although, a clog in the fuel line would cause misfires in all the cylinders, but its good to check for peace of mind.
Clogged Injector:

A clogged injector can also cause misfires. For this test, I pulled out the injector rail with the injectors connected and cranked the engine. I was looking for the fuel exiting the injectors on the tissue placed underneath. It seemed like all the injectors were firing. However, when I repeated the test, the injectors on bank 2 did not fire. On repeating the test for the 3rd time, I found that all of them firing again. This is concerning because intermittently occurring issues are the hardest to diagnose. There might be something wrong with the wiring or the computer.
10. Visual ECU inspection

Watermarks: Over time water can cause rust on the metal parts. This can cause the metal parts to break causing.
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Short Circuit: While the ECU is covered under a properly protected weather box, water has entered at some point due to a leak or temporary removal of the ECU.
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Insufficient supply of current to a specific cylinder causes the misfires.​
Physical damage:
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Any physical damage to the outer body and hence the motherboard can cause unpredictable behaviour.
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Broken pins at the connector end can cause missing signals essential for the right vehicle performance.
Results: From the visual inspection the ECU seems to be alright. No marks no water signs.
11. Upstream O2 Sensor

​Although unlikely the pre-cat oxygen sensor might be causing the problem since is not reflected on the OBD scan. To eliminate the concern, I loosened the O2 sensor while the vehicle was running and checked for performance differences. Loosening the O2 sensor enough to let the outside air have enough space to move in was enough for the vehicle to show an evident difference in performance. This rules out the bank 2 upstream O2 sensor from being the issue.
12. Cam Timing Adjuster Solenoid
This diagnosis is to check if the cam adjuster solenoid on bank 2 is operating fine. I followed three steps to ensure it worked fine.
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Resistance

While the exact value of the resistance through the solenoid is unknown, I use the solenoid of working bank 1 as a reference and compare. The result was that both the solenoids were at the same resistance. While the exact value of the resistance through the solenoid is unknown, I use the solenoid of working bank 1 as a reference and compare. The result was that both the solenoids were at the same resistance.
2. Swapping solenoids
The next way to verify is to isolate the solenoid and see if the issue follows. This can be done by swapping out the cam adjuster solenoids of the two banks and seeing if the misfiring now happens at bank 1. On swapping the solenoids the issue still stayed with at bank 2 indicating the solenoid is not the problem.
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3. Cam adjustment degree

In this test, I check the cam adjustment angle with a scan tool. The cam adjustment angle when the vehicle is idle should be between -3 0KW and 6 0KW. It seems like the values for both the banks are in the range but have a 3 0KW difference between them (-5 0KW and -2 0KW for banks 1 and 2 respectively). While I don’t know what the defined specification of the adjustment should be, it might be worth getting both aligned to the same angle and observing the difference. But before that, it might be worth checking the cam adjusters themselves to see if that is the reason for this misalignment.
13. Plugged CAT

Noticing some exhaust smell and my friend Niko pointed out the exhaust coming out of the intake. This is an acute case of plugged catalytic converter. He removed the oxygen sensor on the misfiring bank and violla, misfires vanished. This is a moment I will never forget, my first success after months of disappointing results.
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Reason: Since the exhaust was completely plugged, exhaust air was pushing back on the exhaust valves at the bore, This caused cylinders to not produce enough vacuum to pull in air and not combust properly. The exhaust air found its way back to the intake.
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The previous test on the oxygen sensor did not bring out the same results because the O2 sensor was only loosened and not removed completely. Since the CAT was completely plugged, the loose threads in the sensor fitment were not enough to let all the exhaust from 3 cylinders out at the rate it was supposed to. The pressure of the exhaust out of the O2 sensor hole was very strong and given the strength and heat, it is not wise to let it on for long. There are electrical wires on top of it that can melt. Considering the age of the car finding a harness would be just as hard.

Measuring blocks 15 and 16 gives the misfire counts in bank 1 and bank 2. All indicating 0 is very satisfying to watch. Given the condition of the CAT, air pressure cleaning would not work. The cascading effects of misfires and heat from incomplete combustion caused the CAT to melt into a plug. Hence a 'plugged' CAT.
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The vehicle had gone into limp mode because of the misfire issue. It is quite possible that the vehicle would cut off fuel when pushed into drive. The reason is unknown but the car seemed to drive with the issue gone, so problem number 7 was also resolved.
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Solution: The only solution is to get a new CAT. The car has 2 banks, the CATs from both banks merge into a muffler/resonator before splitting into 2 exhaust tips. All I need is the driver-side CAT which has the preCAT and catalytic converter.
Problems
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Oil leakage on the Bank 2 valve cover
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Misfire on bank 2: Cyl 4,5,6
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Bank 1 downstream O2 sensor
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Rocking front axle
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Vacuum Leak
-
Foggy headlamps
-
Ignition cut off when gear changed into Drive.
Error Codes
-
P0300 – Generic Misfire
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P0304 – Cylinder 4 misfire
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P0305 – Cylinder 5 misfire
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P0306 – Cylinder 6 misfire
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P0141 – O2 Heater Circuit (Bank 1 Sensor 2)
14. Headlight Cleaning

Headlights = super important. Due to oxidation, there is a layer that forms on the headlights making it super hard to see. A very stright forward fix with some scrubbing with some sandpapers and soapy water to make sure the surface is nick clean and smooth followed by a little buff with a wool attachment that helps with heat and cleaner finish. Did not have polish at the time hence had tto stop at this point, but the results were still as satisfying as expected.
15. Valve Cover Gasket

Found some grey smoke from the back of the bank 2 right around the exhaust. This was very faint smoke and hard to see if you weren't looking for it. Two potential sources of the problem can be 1) exhaust isn't properly sealed or a bad exhaust gasket, or 2) engine oil is dripping on the exhaust from the valve cover causing the smoke. The latter seemed very reasonable since the valve cover had been on and off while diagnosing the misfire issues. An easy fix to that was to replace the valve cover gasket and apply some CurilT gasket sealant/gasket maker.
16. Transmission Range Sensor

The transmission range sensor itself is straightforward to replace. The real challenge is getting to it in the B5 v6 engine. The 6mm hex tip on the top bolt in the transmission bracket bolt was easy to stip due to the age of the bolt and the tough angle to get to it. There were suggestions to lower the subframe to get to the bolt which seemed to be an overkill until there was no other way to access the bolt. What worked at the end of the day was to use a torx bolt with the car on a lift with a long extension. After the bolt was out, it is easy replacement.
17. Auxiliary fan replacement

By far the easiest job on this vehicle has been replacing the auxiliary fan at the radiator and condenser unit. This unit is secured by a tiny Philips screw and rotated in place. The rod running from the hood lock to the base shown in the right securest the harness below it and the wiring runs all the way around the radiator to next to the power steering pump fluid. A quick 10 mins should be enough to replace it if the vehicle is in service position.
18. Fog lamp replacement

Since I had the vehicle already in service position, I changed the fog lamp from behind the bumper but it is almost as straightforward from the front. Once the bulb wires are disconnected, a strong twist to the cap of the fog lamp housing allows to access the bulb. The bulb is secured in place with a metal wire very similar to retainer pins. A little bit of strength may be required to get it off to put the new bulb.
19. Coolant Leak
Step 1 to fixing a leak is to trace it back to the source, considering the coolant system is spread all across the engine bay since the vehicle is a V design. Although coolant leaves a trace, however in this case, it was hard to track it since all that was visible was a puddle under the car and some droplets on the engine oil sump.
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Adding a dye to the coolant helped to enhance the trace a little better and with a UV light, working backwards through the image shown below, some traces of the coolant were found right under the crankshaft pulley, and then some traces were found behind the tensioner pulley which is right under the thermostat and some traces confirmed the leak originating at the thermostat housing.

This car had a plastic housing and with time it is known to brittle up and fail to seal, even with the thermostat o-ring. Getting to the thermostat and the housing is a complicated job since the timing belt has to be removed to get to it. So I also did a timing job and covered it next. Also, while the coolant was removed from the system, a few other parts were replaced.

A radiator hose connecting a valve post radiator feeding into the thermostat housing was swollen as I show in the top left of the image above. Autoshops did not have the right diameter for the tube so had to special order the part. I also replaced the plastic thermostat housing with the metal housing that came from eBay and shipped from Europe since only the European versions of these cars had the metal parts. A new water pump was also installed since it is recommended. The stubborn fibreglass gasket around the water pump was hard to remove with a gasket scraper but getting a blade made it easy enough.
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Checked for leaks at the end by pouring in distilled water and running the engine for a minute. Since the vehicle was in the garage for the duration of the job, water did not freeze, hence I could go by without using antifreeze. This helped because I wanted to check for leaks and needed a transparent liquid to utilize the residual dye in the system.
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It is important to bleed out the air from the heater hose going into the cab. This ensured no air pockets are stuck in the system which may cause underfilling of coolant and hence heating issues. This is done by pulling the radiator hose until a provided pinhole is exposed to coolant. After filling, the coolant reservoir is lifted until some coolant is squirted out of the pinhole.
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I let the vehicle sit for a few days while completing the other job and running the engine for a few minutes (high idle for 3 mins and idle until the bottom radiator hose was hot), did not show signs of an existing leak.
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The coolant leak was hence fixed.
Key Programming

It was weird to have the remote key suddenly not working after replacing the battery in it. While it is not very difficult to reprogram the key, it might take a few attempts with a few permutations and combinations to get it right. Instructions here can help. There is a requirement of having at least 2 keys and up to 4 keys can be programmed for a car. Or at least that’s what the instructions mention.
PCV Valve Change
This ma build up the pressure and can cause