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Thread: 01 B5 S4 Alternator/Electrical Problem

  1. #1

    Default 01 B5 S4 Alternator/Electrical Problem

    I was about to start driving my car home from work on one of the consecutive mid-40 degree days we had here in Adelaide at the start of the year when upon startup got a alternator failure warning popup on my ColourMFA along with the voltage gauge constantly going up and down between 12v and ~16v plus the standard red battery light on the dash indicative of an issue with the alternator. Car seemed to run well enough and I decided to risk driving it home. Unfortunately got about 15km into the 45km drive home and started noticing the car progressively start to lean out on my wideband AFR as I was driving along, more than likely due to the battery volts dropping and being unable to maintain the voltage to the fuel pump. Decided to play it safe and pull over and get the car towed home to not risk damage to the engine.

    Fast forward to pulling the old alternator (a Bosch unit) out of the car and installing a brand new one (a Valeo unit) from FCP Euro, same pulley size and shape and both 120A units so afaik they're interchangeable. Started the car and I'm still getting a warning saying alternator failure on my ColourMFA along with the red battery light however no voltage going up and down on the gauge anymore, the voltage when the car is running is sitting just above 12v which says to me that it's running on the battery alone and not the alternator. I double checked both of the grounds in the engine bay (one on false firewall behind coolant reservoir and the other that links the frame rail to the engine mount on driver's side) and cleaned the terminals in case that might have been the issue, I also checked the terminals in and next to the fuse box under the steering wheel, all were clean and tight.

    After starting the car a few times the issue went away and it seemed to be running correctly, voltage at 14ish with car running and sometimes no warning lights and sometimes voltage at 14ish and the red battery light again.. after starting it again consecutive times the issue where it would sit at 12v with the red battery light returned so it seems to be somewhat intermittent but not sure of the causes.. Not sure what else could be causing this problem, the battery in the car is only 2yo and holds charge well so i don't have any reason to suspect it, I thought it may have been a ground but I can't think of any more to look at.. Is there something else that could be causing this all together?

    Any advice/suggestions would be appreciated.
    Last edited by Bainos; February 3rd, 2020 at 01:53 PM.
    Current: Nogaro 2001 B5 S4 Avant 6SPD - GET Stage 2+ Tune, Bosch 750cc Injectors, Walbro 450 Fuel Pump, Billy Boat 2.5" Catless Downpipes and Exhaust, APR R1 Diverter Valves, Bilstein PSS9 Coilovers, 034 Rear Sway Bar.

    Previous: Black 1999.5 A4 B5 1.8TQ 5SPD - Unknown Stage 1 tune, Turbo Back Exhaust, FK Coilovers, 710N Diverter Valve, Carbonio Intake

  2. #2

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    Earth wire from the Alternator itself?

  3. #3

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    Quote Originally Posted by Khoa View Post
    Earth wire from the Alternator itself?
    It's my understanding that the alternator does not have an earth wire as the body of the alternator acts as a ground through the mounting points to the engine and thus chassis via the thick grounding strap from the engine mount to the frame rail, unless I am mistaken? Or are you suggesting I add an additional ground from the alternator to the body directly?

  4. #4
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    Quote Originally Posted by Bainos View Post
    It's my understanding that the alternator does not have an earth wire as the body of the alternator acts as a ground through the mounting points to the engine and thus chassis via the thick grounding strap from the engine mount to the frame rail, unless I am mistaken? Or are you suggesting I add an additional ground from the alternator to the body directly?

    Yep correct, alternator windings are internally grounded, if it is a new alternator should be no issue. The output of the alternator is connected to the starter solenoid and then to the battery via a heavy cable. I know it is a pita but may be worth checking these connections to start with. The battery then connects to the remainder of the electrics via bus 30 and on to the rest of the system. From what you have described it sounds like a loose/hot joint. Eliminate the easy bits first then look further afield. I do have schematics somewhere if you need them. Its easy to give advice.... you don't have to get your hands dirty or swear when you skin your knuckles... Good luck
    Current - 2007 B7 RS4 Avant, APR Stage 3, Milltek with Hi Flo Cats, GruppeM intake, Sachs Clutch, Factory Ceramics, JHM Shifter, RS6 FBSTW, AMI & Hi Res RSNE
    Current - 2012 B8 A4, 2.0T Quattro Avant SLine
    Current - 2001 B5 S4 Imola Yellow Avant
    Current - 1989 B3 90 Quattro - 7A NA Engine, (Long Term Restoration Project)
    Current - 1984 WR Ur Quattro

  5. #5

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    Quote Originally Posted by Bainos View Post
    I was about to start driving my car home from work on one of the consecutive mid-40 degree days we had here in Adelaide at the start of the year when upon startup got a alternator failure warning popup on my ColourMFA along with the voltage gauge constantly going up and down between 12v and ~16v plus the standard red battery light on the dash indicative of an issue with the alternator. Car seemed to run well enough and I decided to risk driving it home. Unfortunately got about 15km into the 45km drive home and started noticing the car progressively start to lean out on my wideband AFR as I was driving along, more than likely due to the battery volts dropping and being unable to maintain the voltage to the fuel pump. Decided to play it safe and pull over and get the car towed home to not risk damage to the engine.

    Fast forward to pulling the old alternator (a Bosch unit) out of the car and installing a brand new one (a Valeo unit) from FCP Euro, same pulley size and shape and both 120A units so afaik they're interchangeable. Started the car and I'm still getting a warning saying alternator failure on my ColourMFA along with the red battery light however no voltage going up and down on the gauge anymore, the voltage when the car is running is sitting just above 12v which says to me that it's running on the battery alone and not the alternator. I double checked both of the grounds in the engine bay (one on false firewall behind coolant reservoir and the other that links the frame rail to the engine mount on driver's side) and cleaned the terminals in case that might have been the issue, I also checked the terminals in and next to the fuse box under the steering wheel, all were clean and tight.

    After starting the car a few times the issue went away and it seemed to be running correctly, voltage at 14ish with car running and sometimes no warning lights and sometimes voltage at 14ish and the red battery light again.. after starting it again consecutive times the issue where it would sit at 12v with the red battery light returned so it seems to be somewhat intermittent but not sure of the causes.. Not sure what else could be causing this problem, the battery in the car is only 2yo and holds charge well so i don't have any reason to suspect it, I thought it may have been a ground but I can't think of any more to look at.. Is there something else that could be causing this all together?

    Any advice/suggestions would be appreciated.
    Hot weather and crank position sensors. Hmm when was the last time that was replaced.

  6. #6

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    Quote Originally Posted by smit2100 View Post
    Hot weather and crank position sensors. Hmm when was the last time that was replaced.
    Unsure of when last replaced, not in my 2 years of ownership anyway, unknown before that... Luckily I have a brand new one in a box at home so I can chuck that in. Although I'm not exactly sure if it's related to the original problem at hand unless you think it could be?

    Sent from my Pixel 3 using Tapatalk
    Current: Nogaro 2001 B5 S4 Avant 6SPD - GET Stage 2+ Tune, Bosch 750cc Injectors, Walbro 450 Fuel Pump, Billy Boat 2.5" Catless Downpipes and Exhaust, APR R1 Diverter Valves, Bilstein PSS9 Coilovers, 034 Rear Sway Bar.

    Previous: Black 1999.5 A4 B5 1.8TQ 5SPD - Unknown Stage 1 tune, Turbo Back Exhaust, FK Coilovers, 710N Diverter Valve, Carbonio Intake

  7. #7

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    Quote Originally Posted by Tas_Audi View Post
    Yep correct, alternator windings are internally grounded, if it is a new alternator should be no issue. The output of the alternator is connected to the starter solenoid and then to the battery via a heavy cable. I know it is a pita but may be worth checking these connections to start with. The battery then connects to the remainder of the electrics via bus 30 and on to the rest of the system. From what you have described it sounds like a loose/hot joint. Eliminate the easy bits first then look further afield. I do have schematics somewhere if you need them. Its easy to give advice.... you don't have to get your hands dirty or swear when you skin your knuckles... Good luck
    A might take the battery to get it properly load tested out of the car just to confirm that it's not the cause as that's much easier first. If that comes back okay It seems the front end is going to have to come back off again, frustrating but necessary to easily reach behind the alternator and get to the starter and associated wiring, from underneath it is too tight.
    A loose/hot joint fits the problem just finding it is going to be the hard part. If you could send through the schematics that would be really helpful.

    Sent from my Pixel 3 using Tapatalk
    Current: Nogaro 2001 B5 S4 Avant 6SPD - GET Stage 2+ Tune, Bosch 750cc Injectors, Walbro 450 Fuel Pump, Billy Boat 2.5" Catless Downpipes and Exhaust, APR R1 Diverter Valves, Bilstein PSS9 Coilovers, 034 Rear Sway Bar.

    Previous: Black 1999.5 A4 B5 1.8TQ 5SPD - Unknown Stage 1 tune, Turbo Back Exhaust, FK Coilovers, 710N Diverter Valve, Carbonio Intake

  8. #8

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    Had battery load tested externally from the car and it came back good which now rules it out as a culprit. Next task (most likely this weekend) is to pull the front end off (again) and remove the alternator to get behind it to inspect all associated wiring to it and the starter and also check for continuity/voltage drop along the wires. Any suggestions of anything else I should be looking at?

    Another thought, after installing a new alternator is there any special process that should be followed regarding coding in VCDS or clearing DTCs or something else (i.e. complete discharge of system) besides physically connecting the alternator and plugging in the associated plugs/wires that should be done so that the ECU knows there is a new one installed? I connected the new alternator up the same as the original and have cleared the codes a few times now but just wanted to check in case I have missed a crucial step.

  9. #9

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    With some further investigation, upon starting the car up it will idle at 12v on the voltage gauge but as soon as i rev it up to above 1500rpm just once the needle moves up to around 14v as if it was running correctly and then remains there until the car is shut off again and then repeated for each consecutive start. The red battery warning lights comes on upon startup along with the alternator warning on the colourMFA, and both stay on even once voltage has increased. It might be worth mentioning that the car starts each and every time without struggling which indicates to me that both the starter and battery are good? I did manage to start and drive the car a few times and it runs perfectly fine without any warnings and the voltage goes straight to around 14v even at idle but then after more consecutive starts back to getting the warnings.. Potentially thinking that the issue could be related to the alternator exciter wire?

  10. #10

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    Without relying on in-car gauges for a minute, using a DMM, whats the battery voltage before you start it?. What is it when idling? If you drive for 15 mins, what is it using the DMM before you shut down and say 10mins after shut down. Obviously the in-car gauge staying at ~14v is what you want. I'd be wanting to know if my problem was the battery wasn't actually being charged or the gauges were saying it wasn't being charged.
    C5 RS6: APR, Milltek & Wagner -- B5 RS4 : tastefully modified -- Audi 1.8 quattro 132 Kw -- UNIMOG 404 TLF8

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