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Discussion Starter · #1 · (Edited)
CEL, codes P0171 and P1136 - diagnosis?

CEL is solid, not blinking. Just popped on this morning after I was up to temp, didn't blink at all...solid right away. Cannot dig around in engine bay while at work, during lunch Bob at LOTR (Dallas indy) ran VAG-COM and those codes popped up.

P0171 - System Too Lean
P0303 - Cylinder 3: Misfire Detected
P1136 - System Too Lean

Original vac lines, after searching I am guessing the L-hose behind manifold is the culprit:
http://www.passatworld.com/forums/4...ure-control-valve-replacement.html#post820906, and
http://www.passatworld.com/forums/4...ussion/196049-engine-misfire.html#post1184076

Further down in 2nd thread it's mentioned that ICM issue is usually Cylinder 2, since mine is Cylinder 3 hopefully it's just that L-hose. Tech at LOTR did not see any immediately noticeable probs, vac lines look OK - but couldn't check the L-hose on a hot engine given proximity to manifold.

Thoughts on any other potential culprits? TIA

Btw, kicking myself...just the other day I said "you should buy one of those $15 VAG COM cables off ebay". Bob charged for hooking it up and running codes, but he has helped me diagnose a few other issues without pay before - so I'm fairly OK with it. Next time heading to AutoZone, though. :p
 

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Discussion Starter · #3 ·
Past couple mornings have been odd. RPMs on startup are normally above 1,000 especially in the cold, then I'd wait for them to drop to about 800 or so before heading out (quick warm-up).

Since the CEL has been on, cold start hangs around 800 RPM. Is this a result of the vacuum leak? Still haven't had a chance to inspect the L-hose, it's dark when I leave in the morning and dark when I get off work. :(
 

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Discussion Starter · #5 ·
Light back on this morning. :( Never checked the L-hose, get to do that tomorrow morning - boardwalk VW stealer in Richardson is open xmas eve, surprisingly.

Inspection is past due, but I am going on a trip next week and won't be back until 2012. Hopefully it's the L-hose or the CEL goes off again so I can get that done. :)
 

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I just went through a hell of a time trying to diagnose my own CEL. In order...
CEL comes on and off for a few days then stays on for good. Everything seems to run fine.
After about 3 months I borrow an OBD-II from O'Reiley's
OBD-II gave 7 different codes. 4 engine individual cylinder misfire, one generic misfire code, one lean condition code, and one fuel cap loose code.
Replaced 4 coil packs, air filter, cleaned MAF, and tightened gas cap.
Cleared all codes. CEL now off. Seems to run very smooth.
Two days later light comes back on. Still seems to run smooth as silk.
Borrowed OBD-II again (from O'Reily's) and this one had trouble establishing connection. Dinked around with it in the parking lot for a while and found that connection worked best when engine ran.
Cleared error code while engine running. AS SOON AS I PUSHED THE ERASE BUTTON, CAR RAN LIKE CRAPOLA. Instantly.
Drove home and in my driveway, 4 miles later, CEL started flashing.
Called towtruck and a week later he found a big vacuum leak in a fitting behind the valve cover.
He fixed it, cleared the codes and it purrs like a German kitten.
He was a really nice mechanic and a good guy. He only charged me $350, which included the tow.
A few days later I brought him and his wife a Christmas card, a home made loaf of bread and a $40 tip.
I think it pays to have a good mechanic.
 

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OBD-II gave 7 different codes. 4 engine individual cylinder misfire, one generic misfire code, one lean condition code, and one fuel cap loose code.
Cleared error code while engine running. AS SOON AS I PUSHED THE ERASE BUTTON, CAR RAN LIKE CRAPOLA. Instantly.
A boost/vacuum leak will throw MAF-based fueling calculations off. From when the leak first begins, and as the leak gets worse, feedback from the #1 O2 sensor will allow the ECM to learn and adjust long term fuel trims to keep your air/fuel ratio where it should be. The ECM learns to compensate for the hardware failure. That will get you the 5 misfire codes and the lean code.

When you clear codes, you also reset the learned fuel trims back to zero. At that point the ECM is back to delivering straight MAF-based fueling without the learned corrections. The vacuum leak is still causing a lean condition (now uncorrected) and the car will run like crapola.
 

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Discussion Starter · #8 · (Edited)
Welp, is this the L hose that is common culprit for these 2 codes? Haven't removed, but felt around and there isn't an obvious split that I feel on the bottom. Top looks fine.



Anything else that could be the cause here? Should I wrestle off those one-time clamps to inspect?

The ends don't really look like this dude's, is that just from the clamps or am I looking in the wrong place here?
 

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Discussion Starter · #10 ·
CEL went off next start after tinkering with that L-hose and a couple of the check-valves. Looks like last original check valve I haven't replaced is in the vicinity, would that throw the CEL?

None of the other ones did...didn't check for too much play on this one b/c I didn't want last original to break it if it wasn't already busted. Damn things get crazy brittle.
 

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Discussion Starter · #11 ·
Man this is frustrating. Mostly b/c my inspection is past due and car won't pass until I figure this out. Really don't want to take it somewhere, at this point I am guessing it's just a regular vac line - L hose appears in tact and I checked all one-way valves, etc.

Just for my future reference since I'm out of time today:
http://www.passatworld.com/forums/4...46-please-help-find-4-th-vacuum-hose-awm.html
http://www.passatworld.com/forums/6...38-diy-how-replace-1-8t-awm-vacuum-hoses.html
http://www.passatworld.com/forums/4...3294-b5-5-awm-vacuum-diagram.html#post2682956
SVH™ By the Foot : HoseTechniques Silicone Turbo Hose, Buy Direct from Manufacturer, Best Quality / Best Price - Hose Techniques established 1983 - Quality, Performance, Style
 

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Discussion Starter · #12 · (Edited)
All the vac lines feel decent - ones underneath the intake look like a bitch to replace, too. Surprised, everyone mentions they're braided lines...mine are rubber, think I saw somewhere that 2003 was year they switched. Used this thread to locate: http://www.passatworld.com/forums/6...38-diy-how-replace-1-8t-awm-vacuum-hoses.html

Is this the end of bottom one that runs length of the engine then goes underneath to DV? Just inside the passenger wheel?



If so, mods may want to put pic in the thread.
 

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Is this the end of bottom one that runs length of the engine then goes underneath to DV? Just inside the passenger wheel?
Yes. That is the bottom end of that hose where it connects to the Diverter Valve. On your year engine, I believe the top end of that hose connects to a solenoid tucked under the intake manifold. If you have a hand vacuum pump, you can check from the top end to see if that line and the DV hold vacuum.

I see a worm-screw clamp where a one-time-use clamp used to be. Someone has taken that apart in the past.
 

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Discussion Starter · #14 ·
Thanks. No hand vac pump handy, I live in an apartment. :p

Can't view pic from work, any chance whatever that is came loose and is causing CEL? Presumed only the vac line could cause lean code so I did not bother past confirming it was connected and line looks OK.
 

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Discussion Starter · #15 ·
Quick question: Does the fact that CEL is intermittent point to any particular area in the vac system? Seems if it were a gaping hole somewhere CEL would be constant, probably just a small leak/clog somewhere.
 

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The intermittent CEL suggests the fault is creating a condition borderline to the limit that triggers the CEL or that the fault itself is intermittent. Or in other words, it could be wavering on the edge or on-again-off-again.

Your 04 AWM has no ICM.

Have you tried swapping the coilpacks around to see if the misfire code moves with the coil or stays with the cylinder?

140,000 on the original O2 sensor? It may be time to replace it. Data from this sensor is used to fine-tune fueling and learn long term fuel trims.

It'd be good to see what your learned fuel trims are. If the Additive value is way off, look for something leaking manifold vacuum. If the multiplicative value is way off, the MAF may be contaminated or bad.
 

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Steve, IIRC, my 04 AWM had the same nice stamped worm gear clamp. My car had 17K on it when bought too. I assume it to be OE on that piece.

Doyles, try pinching the hose that connects to the intake mani right under the L Hose. It goes to the PCV. If the PCV or "bleeder valve" plunger dislodges internally, you will get on and off CEL as sometimes it makes a seal and other times not. Do you hear anything hissing while running and listening under the hood?

03+ got the nice almost indestructable rubber lines. 125K and they still look new to me.
 

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Discussion Starter · #18 ·
Have you tried swapping the coilpacks around to see if the misfire code moves with the coil or stays with the cylinder?
Believe a misfire did not show up on OBDII printout from botched inspection - just the lean codes. Will double-check at lunch break and update.

It'd be good to see what your learned fuel trims are. If the Additive value is way off, look for something leaking manifold vacuum. If the multiplicative value is way off, the MAF may be contaminated or bad.
Fuel efficiency itself is actually fine - this fill-up was better than previous. 24.484/gal most recent tank, prior was 23.869. Have an app that tracks it.

Presumed if the fuel trims were off I'd be getting worse mileage? I did more hwy driving on recent tank so not terribly surprising, but it was still mixed w/ plenty city. Just happened to be going further distances within Dallas than usual.

Doyles, try pinching the hose that connects to the intake mani right under the L Hose. It goes to the PCV. If the PCV or "bleeder valve" plunger dislodges internally, you will get on and off CEL as sometimes it makes a seal and other times not. Do you hear anything hissing while running and listening under the hood?

03+ got the nice almost indestructable rubber lines. 125K and they still look new to me.
Will do next chance I get. Don't recall any obvious hissing, would have focused on that area if so.

And yeah, vac lines look fine - which is actually kinda disappointing, I was hoping swapping them would be the fix. :p Opted out after inspecting, hope they last to 250k! (personal target for the car)
 

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Fuel efficiency itself is actually fine - this fill-up was better than previous. 24.484/gal most recent tank, prior was 23.869. Have an app that tracks it.

Presumed if the fuel trims were off I'd be getting worse mileage? I did more hwy driving on recent tank so not terribly surprising, but it was still mixed w/ plenty city. Just happened to be going further distances within Dallas than usual.
The MAF measures the incoming air. The ECM calculates how much fuel to deliver based on that measurement (then factors in the learned trim). The engine burns the mixture. The O2 sensor looks at the results. The ECM adjusts fueling based on the O2 sensor feedback.

If the ECM always finds itself correcting richer or leaner, it "learns" this. Lets say it always ends up needing to add 1% more fuel than what the MAF based calculations predicted. It will then set a trim value of Plus 1%.

The system can go out of whack, but the engine management system will do its best to correct and keep fueling optimal. If it sees that it has to implement extreme corrections to keep things on the mark, it will let you know by lighting up the CEL and storing a descriptive trouble code. So you can get a lean code and still get normal mileage because the engine management system is doing what it can to keep everything dialed-in as best as it can.
 

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Discussion Starter · #20 · (Edited)
Interesting. Bought a cheapo VAG-COM cable b/c of all this that I have yet to try out, hopefully software can advise fuel trims?

FYI, scan on 12/5/11 thread start was probably the first since previous inspection 14 months ago - no misfire in the recent 1/24/12 scan. 1,521 miles clocked between them...misfire was probably unrelated. Here are updated codes from 1/24/12 scan:


17544 P1136 001
Bank1, mixture adaptation (add)
System Too Lean
static

16555 P0171 004 -- note this was on first scan too, forgot to include in OP
Fuel Trim, Bank1
System Too Lean
static

16891 P0507 001
Idle Control System
RPM Higher Than Expected
intermittent


CEL went off again last night, still off on my drive to work this morning.

If VAGguy's PCV bleeder valve test yields nothing I may see if PZ can take a look, seems this is getting over my head...no clue why CEL is intermittent. Hope it's nothing blatantly obvious, not sure my pride could handle that. :(
 
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