[diagnosticstruggler]

Thanks so much for any insight I can get on this issue:

I have a sudden no start situation on a 2004 VW Passat, approx 125,000 miles. An independent mechanic did a diagnostic for me up to a cylinder compression test which showed virtually no/very low cylinder compression on all cylinders (~10 PSI) and noted that he didn't see any readily obvious timing belt issue. In the end, he believed that I likely had a more serious engine issue that was probably more expensive than the cost of the vehicle to fix, but that he had limited equipment to check further (mobile mechanic).

I then took it to a local San Francisco VW Dealership (Royal Auto Group) who told me they would charge me a $265 diagnostic fee to identify the issue. I figured that the cost of the diagnosis, if it gave me a solid answer, would be worth it,

I told the dealershi about the independent mechanic's findings of low compression in all cylinders, as well as that I had an timing belt kit installed in 2020 / 20,000 miles ago. They have quoted me around $850 to replace the Crankshaft Position Sensor and when I bring up my concerns about whether the low cylinder compression may indicate more serious engine issues, they seem to indicate that they can't do any further diagnosis without me first agreeing to replace the sensor.

Would the mechanic be able to do any further engine diagnostics and would a Crankshaft Position Sensor be the extent of the issue if I also have low compression in all cylinders? I'd be extremely appreciative of any advice any of you could provide and how to best follow up.

 

[AndreasPassat]

What engine do you have, 1.8t or a V6?
Was the engine running before? Maybe a little more history or back story would be helpful.

I personally can't believe any mechanic would want to replace a Crankshaft Position Sensor when all cylinders are at no compression, unless they are looking to steal your money.
Seeing as you have no compression this a mechanical issue.
A Crankshaft Position Sensor is electronic device which has zero effect or bearing on a strictly mechanical issue.
Checking of the timing marks would be my next bit of advice. It's my guess that something catastrophic has happened like the timing has somehow gotten way off and now all of the valves are bent.

 

[Hirnbeiss]

Hmm, taking an old dog of a car to an Audi dealership in the most expensive part of the US sounds like an exercise in quick cash erosion. Given the $850 quote for replacing a sensor that is easy to replace and is probably not the problem is a red flag. You agreed to $265 for a diagnosis, which I don’t think they’ve provided. I think you need to talk to the guy’s manager and say:
1. What codes did you find?
2. Can you confirm the low compression reading?
If 2 is a “yes”, obviously the ESS is a waste of money. If 2 is a “no”, then the codes should determine the next steps.
If they won’t do a 2, tow the car away. There is a member on here, Ellie, from the Bay Area who had good luck with her mechanic.

 

[PZ]

A compression test needs to be done on a warm engine. If you run one on a cold engine that would not start, you should add a tbsp of oil to each cylinder. If the scan showed a bad ESS, have the mobile mechanic replace it with one from the local parts store. If you have any mechanical skills (oil change type), you can change the sensor yourself on a 1.8T.

 

[ylwagon]

A compression test needs to be done on a warm engine. If you run one on a cold engine that would not start, you should add a tbsp of oil to each cylinder..

True, but a waste of time (and oil) on an engine with essentially zero compression. Assuming that the diagnosis on compression was correct, that engine will sound like a whirring sewing machine when attempting to start, with none of the usual changes in frequency caused by compression bumps.

 

[PZ]

Yes, but an engine that does not start for another reason may have washed the oil off of the cylinder walls and shown an artificially low compression reading.

 

[Hirnbeiss]

You are not wrong, but a “sudden no start” will not be due to ring wear.

Something tells me we’ll never know the final answer ...

 

[ylwagon]

Yes, but an engine that does not start for another reason may have washed the oil off of the cylinder walls and shown an artificially low compression reading.

What I mean is that an engine doesn't go from say 150 PSI on all cylinders to 10 PSI or even zero because the rings are dry, as Hirnbeiss suggests. Something catastrophic occured, such as the crank sprocket key shearing.

 

[Tomvw]

I would say this guy's main problem is his/her brain, and the next problem is a very low phone battery.

 

[vwdoc1]

Yes posting more information can be helpful in providing you with better solutions. If you have a 1.8t engine and you developed a sudden no compression engine then your camshaft timing might be off/jumped and it may have damaged some of the intake valves in the cylinder head.
If the camshaft chain stretched and its tensioner failed possibly due to lack of oil pressure then the camshafts might not be timed to each other.
This can be determined by visual inspection after removing the valve cover and engine timing belt cover. It could even be an engine sprocket that has lost its alignment tab which caused some engine valve damage.
Go back to the basics and check the timing belt of the engine and confirm TDC with the #1 piston.
It should not be difficult to determine what is wrong and why it happened.
Good luck!