My 2018 1.6 TDI Octavia has rough idle after warm startup. Revs go up and down for a while until the engine runs smooth. I noticed that alternator load jumps to +90% when this happens. I can also make revs jump up and down if I switch heated seats on and off.

 

What causes high alternator load this way after startup? I replaced the battery couple months ago and coded the new battery. Alternator voltage is 13.7 - 14.1V. 

 

https://youtu.be/2R948TvNPoE?si=59iSaXdj7JY5IzaU

Edited 27 May, 20242 yr by Lare111

My thoughts are that you have a potential low battery problem or a parasitic load on the electrical system that would definitely cause this symptom.  The alternator is working double-time just to keep up.

Switch off the car; latch the bonnet latch (and potentially the door latch) and let the car go to sleep.

 

You need an amp clamp multimeter.  If the draw is more than between 20-35mA at sleep you have a parasitic draw.  There will be a code stored for a device not able to go to sleep in the diagnostics code scan.

 

Also worth doing a CCA test on the battery.  If the battery is dying, and exhibits low voltage, you will also get problems.

 

Just seen the battery replacement....did you code in the new battery?  If not, this will also be the source of your problem.  The alternator will refuse to charge the battery until the battery is coded in (EFM/AFM battery)

1 hour ago, varaderoguy said:

My thoughts are that you have a potential low battery problem or a parasitic load on the electrical system that would definitely cause this symptom.  The alternator is working double-time just to keep up.

Switch off the car; latch the bonnet latch (and potentially the door latch) and let the car go to sleep.

 

You need an amp clamp multimeter.  If the draw is more than between 20-35mA at sleep you have a parasitic draw.  There will be a code stored for a device not able to go to sleep in the diagnostics code scan.

 

Also worth doing a CCA test on the battery.  If the battery is dying, and exhibits low voltage, you will also get problems.

 

Just seen the battery replacement....did you code in the new battery?  If not, this will also be the source of your problem.  The alternator will refuse to charge the battery until the battery is coded in (EFM/AFM battery)

OP says it was coded.

I fixed the issue. The car tries to use the battery as much as possible to save fuel. Alternator isn't being used apart from engine braking (recuperation). When the car eventually has to charge the battery, it will do it in 150A pulses. This causes the idle revs to jump up and down. The engine has hard time keeping up with the 150A alternator load while maintaining steady idle. 

 

I solved this by coding the battery again. I have EFB battery and used EFB coding but this time I chose AGM coding. When I saved the settings, I immediately heard that idle changed. Now there's no more pulsating idle and charging is much more stable. I don't know if the EFB coding in my car is "broken" or if it just doesn't like EFB batteries. Or maybe charging the battery in pulses works faster. To my knowledge, EFB and AGM are pretty similar so I can use AGM coding without damaging the battery. And I really prefer having smooth idle rather than pulsating revs and shaking car. 

 

Even the Skoda authorized service didn't know what caused my rough idle. Fortunately I have my OBD11. I was worried that I might have bad injector or high pressure fuel pump but in the end I only had to change one setting to fix the issue. It took me a while to find the culprit though.

Edited 28 May, 20242 yr by Lare111

Nevermind. The issue came back. 

 

When I start the car with a warm engine, alternator doesn't charge at first. When the charging starts, it fluctuates between 0A and 150A. This also makes idle revs go all over. I doubt it's a mechanical fault with the battery or alternator since turning for example heated seats on causes stable charging and smooth idle. But it seems like something is telling the alternator to charge pulses after the engine has been started...

1 minute ago, Lare111 said:

But it seems like something is telling the alternator to charge pulses after the engine has been started...

These cars have a variable charge system designed to keep the battery no more than 80% charged, so the charge rate and the charge voltage varying is normal, whether that explains how much your idle speed varies I'm not sure.

Just now, PetrolDave said:

These cars have a variable charge system designed to keep the battery no more than 80% charged, so the charge rate and the charge voltage varying is normal, whether that explains how much your idle speed varies I'm not sure.

Yeah, that feature is called recuperation and I tried to disable it. Nothing changed.

 

I can see that usually the alternator only charges when I am engine braking. But I don't think recuperation explains alternator load jumping up and down when idling. It almost seems like the car doesn't know whether to charge or not.

The issue is getting worse. Now I can feel the fluctuating charging even when driving on light throttle. The car hesitates when the alternator suddenly pulls 160A. I even tried another battery but the same isssue persists. The alternator can handle stable 160A load at 14.3V when tested. I feel like the issue is with battery management system or ECU. If I pull the BMS cable off, car runs and charges smooth but then I get start stop fault. 

44 minutes ago, Lare111 said:

The issue is getting worse. Now I can feel the fluctuating charging even when driving on light throttle. The car hesitates when the alternator suddenly pulls 160A. I even tried another battery but the same isssue persists. The alternator can handle stable 160A load at 14.3V when tested. I feel like the issue is with battery management system or ECU. If I pull the BMS cable off, car runs and charges smooth but then I get start stop fault. 

Sounds to me like the LIN charging control signal isn't right - could be the alternator interpreting it wrong or the signal just being generated wrong.

6 minutes ago, PetrolDave said:

Sounds to me like the LIN charging control signal isn't right - could be the alternator interpreting it wrong or the signal just being generated wrong.

What does the LIN mean here? I am wondering if ECU sends the signal to alternator or if there's some other device controlling the charging. 

LIN is a single wire serial connection that carries data to the alternator telling it what charge rate to deliver.

 

If the alternator is suddenly switching to maximum charge rate that suggests to me either the alternator isn't correctly interpreting the data correctly, or the source (can't remember if this is the CAN Gateway or the BCM?) sending wrong data.

 

Of course as it seems intermittent it could be as simple as a corroded connection? Have you tried unplugging the cable from the alternator and visually inspecting the connector and alternator pins for corrosion?

11 minutes ago, PetrolDave said:

LIN is a single wire serial connection that carries data to the alternator telling it what charge rate to deliver.

 

If the alternator is suddenly switching to maximum charge rate that suggests to me either the alternator isn't correctly interpreting the data correctly, or the source (can't remember if this is the CAN Gateway or the BCM?) sending wrong data.

 

Of course as it seems intermittent it could be as simple as a corroded connection? Have you tried unplugging the cable from the alternator and visually inspecting the connector and alternator pins for corrosion?

It happens every single time I start the car. Sometimess the idle starts fluctuating immediately after the startup. Sometimes it takes minutes and I'm already driving the car. Voltage fluctuating happens just once and doesn't happen again until I restart the car. Voltage also fluctuates after start stop has been used. Since it happens only one time after each startup, I feel like it's a software issue. 

 

I have only checked battery connectors and fusebox connectors. I might take a look at alternator connectors tomorrow too. I have my old battery installed right now and I have to switch back to the new one. I am afraid that the car wont start tomorrow with the old battery 😀

 

I also found a document which explains the whole smart charging feature very well on the page 50. If I am correct, the issue could be J533 (Gateway?), J367 (Battery Monitor Control Unit) or the alternator itself. 

 

https://www.vag-technique.fr/ext_files/ssp/vw/SSP_477_Audi_A1_EN.pdf

Edited 8 June, 20241 yr by Lare111

12 hours ago, Lare111 said:

If I am correct, the issue could be J533 (Gateway?), J367 (Battery Monitor Control Unit) or the alternator itself. 

 

https://www.vag-technique.fr/ext_files/ssp/vw/SSP_477_Audi_A1_EN.pdf

... or the wiring and connectors, do NOT assume it has to be a module!!!

I have time booked for next week but I'm pretty confident that authorized Skoda service cannot do much without fault codes. At least I am not paying anything since I have 3 weeks of warranty left. 

 

I looked at live data and I believe Generator Specified voltage value is the one that Gateway tells the alternator to produce. I can control it myself in outcome test too. When the rough idle starts, generator specified voltage value jumps to 14.7V and then battery voltage follows it shortly. I am pretty confident that alternator is fine. It produces the exact voltage values it should and can produce 160A at 14.4V. 

 

Is the J367 Battery Monitor Control Unit just a small resistor attached to the negative battery pole? I don't think it can break down. I believe this might be Gateway software issue or bad contact somewhere. Maybe service could update gateway module?

Edited 10 June, 20241 yr by Lare111

36 minutes ago, Lare111 said:

Is the J367 Battery Monitor Control Unit just a small resistor attached to the negative battery pole? 

No, it's a small electronic module that uses the cable as the current sensing resistance and generates a data signal.

The issue has not been resolved yet.

 

Today something weird happened. I noticed that the car engine braked harded than usual. Idle RPM was also 1000RPM even though DPF regenerated just yesterday. The alternator tried to charge the battery with up to 100A current which is way too much. Idle increase request fluctuated between stage 1 and stage 2 which also made the idle RPM jumping up and down. Voltage was between 12.2 - 14.7V and battery charge was 87%.

 

Electrical consumption was low. No AC or lights and just radio. When I restarted the engine everything went back to normal.

 

My old Passat had similar issues. Suddenly idle RPM jumped up to 1100RPM and I got start stop fault message. Sometimes lights blinked when this happened. There were fault codes for voltage and broken battery. The issue was bad battery contact. This time I have checked battery contacts but there are more cables in the engine compartment too.

1 hour ago, Lare111 said:

The issue was bad battery contact. This time I have checked battery contacts but there are more cables in the engine compartment too.

Have you also checked where the negative battery cable is attached to the car body?

2 hours ago, PetrolDave said:

Have you also checked where the negative battery cable is attached to the car body?

Yeah. I removed the battery and cleaned and tightened all the contacts. Idle was 1030RPM after test drive and battery was charged with high current.

 

I think alternator connectors should be investigated next. If I cannot find anything wrong with the connectors I might buy a new negative cable with the battery module and replace that. It doesn't cost much.

 

I also need to learn how to check cables with multimeter. I tried measuring the negative battery cable and it showed 5 ohms. I think the battery module has resistor inside.

22 hours ago, PetrolDave said:

Have you also checked where the negative battery cable is attached to the car body?

 

19 hours ago, Lare111 said:

Yeah. I removed the battery and cleaned and tightened all the contacts.

 

I tried measuring the negative battery cable and it showed 5 ohms. I think the battery module has resistor inside.

You only mention removing the battery, that doesn't answer my question about where the negative cable is attached to the bodywork?

 

5 ohms for the battery cable is very wrong, are you sure it's not 5 milli ohms? It is were 5 ohms the the voltage drop when the starter motor engages would be huge and the car wouldn't start.

 

The battery module does NOT have a resistor, it senses the current using the resistance of the negative cable.

The car was investigated last week. Authorized Skoda service said that everything is fine. They just told me to drive.

 

Now the alternator exploded. I noticed that something was really slowing the engine down. Then I heard a popping noise and smelt burning so I turned the engine off. Oil was everywhere and alternator flywheel parts on the bottom.

 

It's good that nothing else was damaged and the engine was still running fine. I also have 5 days of warranty left. I got the car towed to the same useless service shop and they should replace the alternator for free.

On 24/06/2024 at 21:40, Lare111 said:

The car was investigated last week. Authorized Skoda service said that everything is fine. They just told me to drive.

 

Now the alternator exploded. I noticed that something was really slowing the engine down. Then I heard a popping noise and smelt burning so I turned the engine off. Oil was everywhere and alternator flywheel parts on the bottom.

 

It's good that nothing else was damaged and the engine was still running fine. I also have 5 days of warranty left. I got the car towed to the same useless service shop and they should replace the alternator for free.

Where did the oil come from?

9 hours ago, ords said:

Where did the oil come from?

It came from the alternator freewheel. The seal was detached and the freewheel shot all the lubricating oil on to the fuel filter housing. 

Car repair shop refused to fix the alternator for warranty! For some reason battery coding said 80Ah instead of 70Ah. They said it caused the alternator to burn. I have no idea why battery capacity said 80Ah since I coded it several times and I'm 100% sure it was 70Ah. I also doubt 140A alternator will explode if it has to charge 80Ah battery.

 

The shop quoted 1000€ for the alternator replacement. Even though I had the car towed to the shop, I just drove it home without serpentine belt. 2 hours and I had removed the alternator. I can't find anything wrong with the bearing or freewheel. I will get the replacement alternator tomorrow for 265€. I hope it fixes my charging issues. 

 

And the original issue still persist even with the new alternator. Voltage fluctuates between 12.2 - 15.0V after startup and eventually stabilizes...