S4 no start after dead battery and replacing coilpacks
09-25-2014, 04:06 PM
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S4 no start after dead battery and replacing coilpacks
One day running fine, next morning rough running and CEL on the way to work. 10mins later really rough running and limp to work; then limp to mechanic. Mechanic says I need 6 new coilpacks, new plugs and new O2 sensors. Seems a "little" excessive to me (at $1500). I opt to take it home and hook up my VAG cable and do what I can.
Replace 3 coil packs, and decide to wait on the plugs to see if the coilpacks remedy the issue . When I pulled the coilpacks I discovered I need to replace the center valve cover gaskets, so I figured I'd save the plug replacement for that. While waiting on parts and time to work, the batter dies, recharged it and suddenly no start.
No codes on VAG, engine turns over but doesn't catch -- something I've never experienced with this car in 6yrs. Only slight gas smell at tailpipe after cranking, checked all engine and ECU fuses, none blown, connectors on airbox reattached in correct order (brown in front, black in back). I can say I don't hear the fuel pump, but I can't say I remember hearing it before either -- I do remember hearing it in other Audis I've owned though.
What have I missed? Where should I check next? Not having my car hasn't hurt too much yet, as I can get to work in 20mins on PT, but its starting to get cold out.
TIA
Heybiff
Replace 3 coil packs, and decide to wait on the plugs to see if the coilpacks remedy the issue . When I pulled the coilpacks I discovered I need to replace the center valve cover gaskets, so I figured I'd save the plug replacement for that. While waiting on parts and time to work, the batter dies, recharged it and suddenly no start.
No codes on VAG, engine turns over but doesn't catch -- something I've never experienced with this car in 6yrs. Only slight gas smell at tailpipe after cranking, checked all engine and ECU fuses, none blown, connectors on airbox reattached in correct order (brown in front, black in back). I can say I don't hear the fuel pump, but I can't say I remember hearing it before either -- I do remember hearing it in other Audis I've owned though.
What have I missed? Where should I check next? Not having my car hasn't hurt too much yet, as I can get to work in 20mins on PT, but its starting to get cold out.
TIA
Heybiff
10-05-2014, 11:26 AM
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After intermittent searching on other forums, the consensus was: after checking for spark, and gas, or unplugging the MAF, clean the grounds under the coolant tank. Cleaned the grounds, which frankly looked clean already and were tight, and cranked again, and miraculously it caught.
Had big grey cloud and a LOT of vapor until it warmed up, scared me a little. Took it around the block and had the same loss of power and hesitation in 2nd and under power as before. Parked it and pulled the codes and got :
2 Faults Found:
17861 - Exhaust Gas Temp Sensor 1 (G235): Open or Short to Plus
P1453 - 35-00 - -
17865 - Shareware Version. To Decode all DTCs
P1457 - 35-00 -
Did some more checking and it seems the EGT sensors fail fairly regularly. Checked the sensor connection and it was tight and in good condition. Will replace and update. It also took an unreasonable amount of searching to find which side was bank 1 (passenger side in US). It seems a LOT of ppl ask that question, and most only reply "search for it" instead of just answering. One thread had 12 replies to that question with no direct answer beyond "search". What makes it worse is a LOT of the Google links -- specifically AW links are broken. Wow, when did the Interwebs get so harsh?
As an aside, I have not been on AW for a long time, but I remember it was a lot livelier than this in the past. Besides the annoying ads, has something changed that has made ppl drift away?
H.
Had big grey cloud and a LOT of vapor until it warmed up, scared me a little. Took it around the block and had the same loss of power and hesitation in 2nd and under power as before. Parked it and pulled the codes and got :
2 Faults Found:
17861 - Exhaust Gas Temp Sensor 1 (G235): Open or Short to Plus
P1453 - 35-00 - -
17865 - Shareware Version. To Decode all DTCs
P1457 - 35-00 -
Did some more checking and it seems the EGT sensors fail fairly regularly. Checked the sensor connection and it was tight and in good condition. Will replace and update. It also took an unreasonable amount of searching to find which side was bank 1 (passenger side in US). It seems a LOT of ppl ask that question, and most only reply "search for it" instead of just answering. One thread had 12 replies to that question with no direct answer beyond "search". What makes it worse is a LOT of the Google links -- specifically AW links are broken. Wow, when did the Interwebs get so harsh?
As an aside, I have not been on AW for a long time, but I remember it was a lot livelier than this in the past. Besides the annoying ads, has something changed that has made ppl drift away?
H.
Last edited by hey_biff; 10-05-2014 at 11:31 AM.
11-02-2014, 03:05 PM
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After quite a bit of troubleshooting, I ran across a post in the 2.7t forum where someone listed the same issues I had, and detailed some of the same attempts at repair, as well as VAGCOM codes.
After the initial misfire/O2 sensor codes, I replaced the passenger side EGT sensor, that was immediately replaced by the driver side EGT code (I suspect these must be replaced in pairs -- maybe why Audi sells them as a kit? Perhaps new sensors return a signal stronger than a used/worn sensor and the difference between a good old and new on either side throws off the ecu?). After replacing the drivers side EGT, I was left with random misfires and poor performance; but no codes.
If I drove faster than 30MPH or revved above 2.5K I would get misfires and what felt like boost being bled off. Limp mode? I could force a code for misfire, but nothing else. Next step was to start looking for boost leaks -- even though I didn't have them before this started.
The old post on the 2.7t forum related similar circumstances and said he replaced the coolant temp sensor ($10 part back then). Went to dealer, picked up part (now $35 but in stock), removed old, installed new, and instant results! Car immediately revved freely, sounded normal, and no codes. Misfire was still there, but not nearly so noticeable. When I checked VAGCOM, random misfire was back, with effected cylinder. Popped out coilpack, and now am back to normal.
Apparently the sensor can degrade to the point where it sends a bad temp to the ECU, but within specs, causing the ECU to attempt to run the engine rich, and so forth. Because its within specs, no code will be thrown. The only way to check besides replacing the sensor is to read the measuring block in VAGCOM, but how may of us have that troubleshooting info handy? As soon as I snapped off the retaining clip, I knew my sensor was probably the original, disintegrating O-ring and all.
Adding this reply just in case anyone else runs across this issue as well. My goal was not to replace all my plugs/coilpacks if I didn't have to. It seemed odd that so many pricey items would fail all at once when the day before all was well. Might as well have all the info in one place.
After the initial misfire/O2 sensor codes, I replaced the passenger side EGT sensor, that was immediately replaced by the driver side EGT code (I suspect these must be replaced in pairs -- maybe why Audi sells them as a kit? Perhaps new sensors return a signal stronger than a used/worn sensor and the difference between a good old and new on either side throws off the ecu?). After replacing the drivers side EGT, I was left with random misfires and poor performance; but no codes.
If I drove faster than 30MPH or revved above 2.5K I would get misfires and what felt like boost being bled off. Limp mode? I could force a code for misfire, but nothing else. Next step was to start looking for boost leaks -- even though I didn't have them before this started.
The old post on the 2.7t forum related similar circumstances and said he replaced the coolant temp sensor ($10 part back then). Went to dealer, picked up part (now $35 but in stock), removed old, installed new, and instant results! Car immediately revved freely, sounded normal, and no codes. Misfire was still there, but not nearly so noticeable. When I checked VAGCOM, random misfire was back, with effected cylinder. Popped out coilpack, and now am back to normal.
Apparently the sensor can degrade to the point where it sends a bad temp to the ECU, but within specs, causing the ECU to attempt to run the engine rich, and so forth. Because its within specs, no code will be thrown. The only way to check besides replacing the sensor is to read the measuring block in VAGCOM, but how may of us have that troubleshooting info handy? As soon as I snapped off the retaining clip, I knew my sensor was probably the original, disintegrating O-ring and all.
Adding this reply just in case anyone else runs across this issue as well. My goal was not to replace all my plugs/coilpacks if I didn't have to. It seemed odd that so many pricey items would fail all at once when the day before all was well. Might as well have all the info in one place.
Last edited by hey_biff; 11-02-2014 at 03:08 PM.
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