96 Passat w/ Power Loss, DTC 310, and DTC 550

Been having problems with this Passat for a couple months now. Originally couldn't even get to start, but solved that with a new fuel temp sensor in the injection pump.

Now, the problem is intermittent loss of power about anytime, accompanied by either DTC 310 (Catalyst Temp Sensor G20) or DTC 550 (Injection Start Control), or both. Sometimes the CEL sets, sometimes not.

The loss in power can be very intermittent on days above 20 deg F or so, and the car continues to run. If the temp is low, the power loss usually results in stalling. Car can be then restarted with lots of cranking, but immediately stalls again.

The stalling and total power loss seems to be connected with the DTC 550 more often than DTC 310, but I'm not real clear on this. DTC 542 does not accompany DTC 550, so the needle lift sensor G80 doesn't seem to be an issue.

The timing, once I can get the car to run on a good day, is perfect, slightly above center on the graph.

Since this is an intermittent situation, checking the catalyst temp sensor resistance and wiring has never shown a problem. But maybe just because it is intermittent? Also, the DTC 550 code test says to check the Cold Start Injector N108 in Output Diagnostic Test Mode, but am unfamiliar with how to do this. Can this be done on a VAG COM?

Is anyone out there familiar enough with such a situation to hazard a guess as to whether I have a Cat Temp Sensor problem, a Cold Start Injector problem, an ECM problem, or something else? I know sometimes the thing the DTC points to is not always the real problem.

I think you have a combination of problems.

First one, I suspect, is that your mechanical injection pump timing is out of adjustment. With the engine warmed up and idling, go into your VAG-COM measuring blocks, select "basic settings", and check the 2nd and 9th numbers against the graph in the factory shop manual the way you're supposed to. I betcha it's way out of spec. Forget about the "diagnostic test mode", that's not worth pursuing unless you FIRST set the static pump timing to what it should be, you still encounter problems, and you then find that actual timing isn't tracking requested under various speed and load conditions.

The second problem is that you have an issue with the catalyst temperature sensor or the wiring to that sensor. Is that fault code an "open or short to ground", or "open or short to B+"? Either one, combined with your measurements of the sensor which suggest that the sensor itself is okay, suggests a bad connection or a short-circuit because of insulation worn off a wire somewhere.

It is remotely possible that a couple of sensors involved in this share a ground or a power supply somewhere, but I doubt it.

The first step is to get the static injection timing so it's in the upper half of the permissible range in the shop manual, reset the codes, and see what happens.

Thanks for the info, Brian, but I think the timing is OK. Maybe I didn't describe it right in my initial post, but I used my VAGCOM, went into MEASURING BLOCKS, hit GO for BLOCK 0, and then hit BASIC SETTINGS. Word 2 was 55 and word 9 was 120, which looks to be in the upper half of the allowable range. To be honest, the readings did not change hardly at all when I went into BASIC SETTINGS. Am I missing something here? Thanks, again.

Brian, forgot to tell you that the 310 code is:

00310 - CAT Temperature Sensor 1 (G20)
30-10 - Open or Short to B+ - Intermittent

Garry

Hi gbillman, Check the wiring leading to the cat temp. sensors located on the front and rear of cat. It's possible one of those huge fender well ice/snow boulders messed them up. Later!

On my a4, the glow plug light flashes when I'm in the right mode. You've checked that the coolant sensor is putting out the right readings? You should have been checking this anyway before you did the timing check to make sure it's warm enough.

The error about lack of injection control is a little scary though.

Here's a long shot. Looking through fault code charts one obscure possibility is a clogging/dirty fuel filter causing fuel starvation causing DTC 550 (or equivalent). When was the last time it was replaced? Have you been getting fuel at reliable places?

Have you checked all the ground connections you can find for clean and tight?

Thanks, MOGolf. I'll change the fuel filter and see, also check the grounds as you mention. Still need to get under the car and check the two cat temp sensors like Harvieux suggested. We got snow last night and some of today, and just haven't been able to crawl under the car and see. When was the last time the fuel filter was changed? Before I bought the car, so you make a good point!!

VelvetFoot - Yes, the coolant and fuel temps look fine on the VAGCOM. I always check the fuel temp, now, since my run-in with the fuel temp sensor. Both temps read near-ambient right after start-up and then rise as things warm up. The glow plug light flashes on mine, too, in BASIC SETTINGS, so I'm pretty sure I'm working the VAGCOM right. What is scary to ME is that the end of these two DTC troubleshooting trails leads to REPLACE ECM!! Has anyone seen an ECM go out intermittently, causing more than one DTC, and causing the SAME DTCs all the time? What's it take to replace an ECM and can it be done by someone with only a VAGCOM?

I REALLY hope that's not it.

MOGolf, you called it buddy! Fuel filter was causing BOTH those codes! Pulled the filter and drained it into a jar. 50% - 70% WATER!!! My guess is it had never been changed in 140K miles. New filter and those codes are gone.

But now my CEL is lighting up and the Fuel Temp Sensor DTC is back HARD! Will not clear. I just replaced that damn sensor. Took a couple weeks for VW to get it in the US. Any guesses here, folks? Maybe water shorting out the sensor? But is the fuel pump (where the sensor is) upstream or downstream of the filter? My guess would be downstream. In that case, what's the chances water got PAST the filter? I would hope not.

I have fixed a fuel pumps temps sensor due to water contamination in the past. Run MAJOR DOSES of Power Service thrught the system. Also run some Power Service Biocide to kill off any bacteria.

I'll start a new thread describing how to repair it.

DB

Fuel Temp Sensor Repair thread

http://forums.tdiclub.com/showflat.php?Cat=&Board=UBB41&Number=466591&page=0&view=collapsed&sb=5&o=7&fpart=1

DB