Dear members,

 

For some time now, I'm troubled by some strange behavior of my 70A alternator on my 1.4mpi Fabia / AQW. I've visited a few dealerships and mechanics and they all tell something different.

 

Since it's a long story, I'll try to keep it short a possible. The alternator was revised, but the voltage drops to 11.80v when under full elec. load (excl. PAS) when idle (without load 14.2v). Normally the engine would rev up a bit automatically when under full elect load when idle, but now it's doesn't anymore. And something new happened last two weeks (and only sometimes when engine is cold); the battery light stays up after start until I rev up to 1500rpm (no 14,2v when the light stays on).

 

* Alternator tested on bench last week, seemed to be ok.

* All high-amp cables, fuses, connectors and grounding cables are revised to be nearly new (max 0.16v loss between battery and alternator under full load/idle, 0.05v under minimal load/idle)

* The two signal cables (L1 and DFM) at the alternator read 11.5v from the car with the contact on (not running) and the signal cables and connectors look good. Battery light stays off when the alt. signal connector is disconnected when on contact > ok

* No errors found in the VCDS modules.

 

I'm still not sure if the default 70A alternator is too light (since 90A in later models), if the new alternator voltage regulator is 100% (alt. pre-power signal L1 shortage when cold?) and if the DFM signal read by the ECU is correct (since no auto rev up when idle).

 

I need to be sure where the fault lies before I start complaining about an improper alternator revision or when the dealership tries to sell me an expensive new ecu or a complete new wiring loom. I hope someone can help me with this (including finding the correct measurement blocks in VCDS) before I create a complete alternator, charging etc. DIY for this type of car on this forum.

 

Thank you in advance.

 

 

 

Edited 16 August, 20178 yr by Palatinux

Can you borrow a known good battery to try, to see if/how the situation changes.?

I will find the measuring block for alternator load on VCDS.  

Measuring block 53 in Module 01(engine), Fields are Actual rpm, Specified Idle rpm, Voltage (term 15?) and Alternator load(%).

@Palatinux - Have you checked the battery yet? These can cause issues under deep load.

Thank you guys. I forgot to tell about the battery. It's a 44ah budget battery. Replaced last year. Battery was checked with a special expensive (internal indep.?) battery tester last month.

 

- Capacity is around 80-90%, no internal shortage (only Varta Blue next time).

- Voltage 12.5 in rest. 12.4v after a week standing still.

- Clean terminals.

- 17ma parasitic/total draw in rest.

- While hung on a 6ah old-fashion battery loader, it takes 2 amp in the beginning and around 1 amp when full.

- Voltage even drops after a 6 hour drive while on full load.

 

Still, I cannot tell for sure if the battery is the problem. But from what it seems, the battery draw should not really effect the total load. This still does not explain why the car doesn't rev. up a bit on itself while on full load.

 

Thank you Wino, I'll check the alternator load a.s.a.p (the one i was looking for). I remember to have seen the voltage in the past, it matched the voltage on the alternator/cigarette lighter.

When you say that the alternator was 'revised', do you mean replaced?, refurbished?

9 hours ago, Palatinux said:

Battery light stays off when the alt. signal connector is disconnected when on contact > ok

Can you explain what you mean here please?  Are you saying that with ignition switched on the battery light is on, but then goes off if you unplug the connector at the alternator? I'm confused by the description "stays off".

That bit is unclear indeed. Normally when you put the car on contact, the battery light stays on until the engine is running. When I remove the connector from the alternator and put the car on contact, the light stays off.

 

This should mean that the L1 power goes to the alternator and that there is no short-circuit in that line (otherwise the battery light will stay on when the connector is removed)

I see, that sounds right.

 

@Palatinux @Wino - A fast Google search says that a Fabia 1.4 mpi should be using at least an 50ah battery, so this could be part of the issue, particularly given how much current the PAS pump can draw.

I doubt it Ken. The PAS pump can draw very high peak currents, but does so extremely briefly (so that there's no perceived delay between turning the steering wheel and getting the assistance needed), unless driving a particularly slalom-like route.  Going in a straight line it takes only about 3 amps, less than a single headlamp bulb.

 

What I have heard of - but struggle to understand - is one guy who had a normally functioning battery light, and continuity of the exciter (L) connection to the alternator, but his alternator still didn't start up correctly. Replacing part of the blue wire (I forget which part) fixed it.  Ideally, measure the current going into terminal L on the alternator when ignition is on, but engine not running.  From memory it should be around 50mA.  Inserting a multimeter in series is a slight challenge though.

@Palatinux when you checked the wire/connectors, did you try pulling gently on the wires near the gearbox bracket connection, or just inspect visually?

 

@Wino. I've unplugged the connector in front of the gearbox and checked the connections, wires and isolation. All spotless after 16 years. No moisture too.

I forgot the mention that the alternator was first replaced by another revised one before my own alternator was revised (they didn't have another one in stock). The issue of the voltage drop under high load stayed the same in all situations.

 

I just checked the car again after the 6hrs drive last weekend; no errors in the modules. While the engine is not running; Measurement block 53 is 0.2v off to the measured cigarettelighter voltage. The altenator load is 18.8%. But I don't know if this is the last seen average load while the engine was running.

 

I'll ask my dad if he can help me tomorrow to measure if there is 50ma on L1.  Is there any way to measure both signal cables close to the ECU? My ecu connectors have some kit around it, so I'm afraid to break something since it won't come off.

 

p.s. The PAS works a bit faster and better after I cleaned all ground and high-amp wires and fuses on the car b.t.w.

 

 

Only the DFM wire goes to the ECU, the L/blue one goes to the J519/Module 09 controller in the cabin (above clutch pedal position on a LHD drive car, I guess.) I can tell you the exact connector/ pin number later. Edit: see added photo, not the best picture, but easily found on ebay, the unit mounts the other way up in the car, with wires hanging down.

 

You could just unplug the two-way connector at the alternator, and insert the multimeter into the L connection there, not worrying about the DFM wire being unconnected during the measurement. It's a monitoring signal rather than a controlling signal, so I wouldn't expect it to affect this measurement. The engine will not even be running, so the DFM signal will not be available from the alternator. 

 

Edited 16 August, 20178 yr by Wino

Thank you Wino.

 

The engine compartment is sprayed in every year to prevent deterioration of plastics and rubber components. So it might be possible that the isolation is holding a broken wire somewhat together. Had the same with the steel front oxygen-sensor wires in the beginning of this year.  The weak spot on the DFM and L1 wire must then be on the direct right side of the connector in front of the gearbox since this spot wiggles every time you accelerate or shift gears.

 

We'll measure the amps from L1 tomorrow and I'll hook on VCDS to log the 'generator load' while driving. As far as I know, the DFM is a block pulse signal that becomes wider when the load on the alternator increases. High DFM wire resistance may cause the car to think that the alternator is not working very hard, while it's sweating to keep up. This may explain why the bearings of the 'old' alternator where sweating due to overheating and that the modules are not logging an 'implausible signal'.

 

We'll see if this theory applies. I hope that I don't have to replace the whole wire pair since it's not very easy to reach and mend them without a car-lift,

 

 

@wino, wow thanks for the image.  I hope that i can reach the module without having to call in a tiny Asian guy first.

Edited 16 August, 20178 yr by Palatinux
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It's been a while ago and the battery light/alternator worked correctly since then. I logged the car rpms, desired rpms, voltage and alt. load twice (files attached, rename to .csv if required to open in VC-Scope).

The battery indicator light measures 58 mAmps to the alternator.

 

In the log you'll see that:

* The minimal alt.  load with every user off is 18%

* The alternator shoots to 100% load/12V with every user on (no radio) at 800 rpm, but drops around 80%/13.53V at 2270 rpm.  For some reason the car doesn't switch off users or increase rpm by itself while idle though the desired rpms are higher than the actual rpms. I assume that the car will only increase rpms by itself when the battery voltage is below -a- threshold. But only a expert will know this for sure.

 

The battery voltage is around 12.33V after a week standing still (made sure it was charged fully by the alternator the week before / draw was 17ma from battery when car was in rest/locked a few months ago) and it drops to 9.85v while cranking the engine. An expensive internal resistance meter measures a capacity of 90% when the battery is fully charged and it measures no shortage in the battery. I believe that this budget battery was too long is storage without being charged at the supplier > battery sulfation. There are solar chargers that can keep you battery topped (like the velleman SOL5N), but I'm not sure if it can do what it promises.

 

My conclusion is that the alternator is a bit underrated, but not too light for the car if you don't only drive short distances with all users on. A 44ah battery is indeed too light if you drive a lot short trips of leave it parked for (more than) a week.

But I'm still not sure if the alternator is working  correctly or if something else draws too much power since the minimal alternator load is 18%.

 

I visited three local Skoda dealers/specialists, and none of them could make a trustworthy conclusion (besides from trying to sell me a brand new alternator and battery first). I hope someone can help me with this for the DIY if want to put on the forum. A comparable log from another AQW engine or 2000-2002 8v MPI petrol+PAS+heated sidemirrors+front foglights+no AC Fabia model might be enough to make some conclusion that can be used in in the DIY.

 

ptx.txt

ptx1.txt

Edited 11 September, 20178 yr by Palatinux

@Palatinux - The alternator control circuit isn't as "bright" as you think. It just feeds into the idle stabilisation function to maintain the idle speed. That's the same function that lets you "drive" in a fast road queue feet off at idle speed in 3rd gear.

 

Your report on alternator load/function makes me think that the alternator is working about correctly, although it may be under-performing a bit if it's never delivering ~14.4v.

That is good to know. After these few months I only expect that the quite new battery doesn't maintain it's voltage (12.3v after a night), which causes the higher load on the alternator + extra fuel consumption. The headlights dim more when I use the (4 year old) power-steering while parking, even after driving for 6 hours straight before. I guess I should replace the battery before it starts freezing.

 

The alternator light showed up some time ago and I measured 38ma on the system side instead of 58ma > bad connector or cable. The light works flawlessly for a month now, so it leave it there until it get worse.

Replacing the (bad) budget battery (brand Compact) for a new Varta C22 battery tomorrow to see if it solves this strange phenomenon so I can headdesk myself through the weekend for misinterpreting the most obvious.

 

Old battery was 12.12v two days ago, but it still passed all types of battery testers (?). Parasitic draw was only 12ma in car deep sleep mode and the alternator was bench tested ok twice a few months ago.

 

When I started the car this morning, I saw the dashpanel POS test restart while cranking the engine. Alternator charging at 14.3v. The battery light did not stay on/ worked perfectly for almost 3 months now.

 

ps. Under/over voltage can destroy your ECU and other controllers if you are in bad luck. Or if you have this in a Mercedes; instant car fueled campfire. Guess Mercedes invented the 'Firewire' bus/protocol at the same time they used the Bosch CAN bus/protocol for the first time.

 

 

 

Edited 15 December, 20178 yr by Palatinux

@Palatinux - "Mercedes invented the 'Firewire' bus/protocol " is pretty impressive punning in a second language.

Thanks. The headlights don't seem to dim now while using the powersteering. 13.8v at 2200-2300 rpm with the int. blower at max, headlights and rear+mirrorheater on. If you also include fog front+back and highlights, it drops to 12.1V at idle (700-800rpm), which seems quite normal. The int. blower uses the most amps anyway.

 

I'll check on it again in a few weeks to see if it's not the alternator. In that's the case I'm was tricked (twice) by the guys who revisited it. Don't want to spend 90 euro's on a decent DC volt amp meter since I have no other use for it.

 

I never understood why 12V is still the standard in modern cars. Switching to 24V + some 24v-to-12vDC converters or vice versa would reduce the number of wire faults and required amps that need to go trough a wire. And a bit of wire/contact corrosion in the years would have less effect. And I think you could also reduce the size of the alternator and total wire thickness.

 

But more trouble free electronics is nice for consumers, but not for the dealers.

 

Edited 15 December, 20178 yr by Palatinux

Just analyzed previous measurements. It looks like the old battery had a dead cell in certain situations. The old battery cell seem to be ok when it was just charged, but the cell died again within a few hours or under high load.

 

You would almost say a zombie cell. We will see.

 

The new Varta Blue is on 12.59V after 4 days, so I conclude the old battery was bad too. Tried all types of battery testers, none of them found the error on the old battery.

 

My wife's car has the same Varta Blue battery. 4 years old, 8 mile drives daily x around 1600 coldstarts, fully drained a month ago. Still at 90% of it capacity so I must assume it's a top tier battery. And if my wife cannot destroy it...

 

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