danmm7

Some quick background ....
2003 SL55 with 135k miles.
Car runs great but for the last 3 weeks, every single time i start the engine, a red battery light pops on the dashboard.
I get code B1828 ...which points to Relay K57 being bad or "no circuit 61".

- I replaced the relay. It made no difference.
- I am not sure how to test "circuit 61" and there is no info on it in STAR. I am not even sure what/where is circuit 61
- Using a volt meter, i measured the voltage at both batteries at idle. Rear battery in trunk is at 14.25 volts ...... front battery is at 14.60-14.70 volts.

Are these voltage value normal? Isn't 14.60V a bit too high? Can this be the reason for my Red battery light, as soon as i start the car?

My alternator was replaced with a rebuilt Bosch unit about 20k miles ago. I am starting to wonder if the voltage regulator may be bad and causing the red light?


Btw, in the past, i used to get the red battery light from time to time. It would disappear on its own or after i reset the code. Now, it seems like it's been on consistently for week. It doesn't go away.

Any ideas?

pmercury

iTrader: (2)

You have to use WIS for the MB testing info

Speed750

What's the voltage with the key off ? Charging might be a pinch high. I think 14.4 volts is normal when the car is running.

danmm7

With the engine off.... i get the following:

Rear (trunk) battery - 11.93V
Front battery - 12.70V


Ideas?

whoover

11.93 is too low. Sounds like the aux battery needs replacing.

danmm7

This voltage was measured after the car was sitting parked for 24hrs.

This is an AGM battery, purchased from Auto Zone or one of the big chain parts stores. It was installed in March of 2017, so it's 2.5 yrs old.

1. Does it make sense for it to be bad already?...given the age and the 11.9V reading?
2. Can red battery light on the dash be caused by this 'weak' battery? .... the error code points to bad relay or bad circuit 61. It does not mention anything about battery issue.

I can replace it (and i kind of hope the battery is the real issue)...but AGM batteries are not cheap, and if it turns out that it was not the reason for my red warning light...it will be *almost* wasted money.

I will plug my CTEK battery maintainer tonight so the battery is fully charged tomorrow and i will see if the red warning shows up again. This should be a good test.


Thank you!

ray0214

11.93 for 12v AGM battery is only about 40% charged. That’s low, even for a battery sitting for several days

whoover

The CTEK will tell you if the battery will take a charge. But anything below 12.4V is considered essentially dead. Circuit 61 has to do with the charging but the fact that you see 14+V when the engine is on would indicate the alternator and voltage regulator are ok. A resting voltage under 12.4 is always a red flag, and might result in all kinds of spurious codes.

bobterry99

These voltages are perfectly fine, as the specification is for 10.5 to 14.5 volts.

Circuit 61 consists of a single wire from the alternator to the passenger SAM. You can view it's on/off status by viewing actual values of the passenger SAM.

14.60 may be very slightly high -- or not.

Obviously the power supply control module runs a test of the K57 relay. Possibly it measures the current through the coil of K57, and your slightly-high voltage causes too much current and the test fails. But this is pure speculation.

I'd check two things: the status of Circuit 61, and from the power supply module (BNS) actual values I'd see what the voltage at terminal 30a is with the engine idling -- this is the voltage the BNS is measuring on the starter battery.

Speed750

"This is an AGM battery, purchased from Auto Zone or one of the big chain parts stores. It was installed in March of 2017, so it's 2.5 yrs old."

I would find the receipt and take it back asap. It probably has a 5 year warranty so you might get a new one free or at a heavily discounted rate. Even if you can't find the receipt I would return it. Sometimes the stores keep records , bar codes etc.

It's difficult to diagnose electronics if your not starting off with proper voltage.

whoover

10.5V is the voltage of a fully-discharged AGM battery. Maybe the electronics are designed to detect a battery down to zero charge, but an auxiliary battery holding less than 50% charge is not a good thing. Determining whether it can't take a charge (bad battery) or isn't being properly charged (alternator, voltage regulator or wiring) is the first order of business.

bobterry99

An R230 has no problem starting and running with a rear battery at 10.5 volts. That's confirmed by both my personal experience and Mercedes' explicit specification. The attached PDF shows how the vehicle power supply handles a rear battery below 10.8 volts.

That said, if the battery is initially at 10.5 volts and does not charge up fully after a long drive, then there likely is a problem with the battery.

At any rate, on no account will a discharged rear battery trigger a red warning message in the cluster or set fault code B1828. Needlessly replacing a good battery will contribute nothing to solving the problem at hand.

danmm7

So i plugged the CTEK maintainer last night and this morning....after about 12 hours of charging..... when i unplugged the CTEK, the rear battery was showing 12.7 volts on my volt meter.
Later in the afternoon, i checked it again.....(car has not been driven) and the battery was showing 12.4 volts. I will check it tomorrow morning, and i expect it to be around 12 or a bit less, as it was 2 days ago.

I am not against getting a new, fresh AGM battery at some point (not cheap, but if necessary, i will do it), but based on what bobterry has shared, it's very unlikely that a new battery will solve the red light on my dash. Or is there ANY possibility that a weak rear battery can actually cause the red light? The error code certainly does NOT point to a battery issue.

Last winter, on a few occasions when the car was not driven for a week or more, i got a warning in the dash that consumer were offline.... and after 15min driving, everything came back on. It was a separate issue....related to discharged rear battery. Seems to be common with these cars when sitting parked for 1+ week.

More importantly, I was still getting the the red battery light from time to time.... but it was never as consistent as it is now. So i wonder.... what exactly changed, what component fully failed, that i have the red light on now with every start of the car?? Something progressively got worse, i just don't know what. Logically... it may be a battery getting worse with time, but again, the error code does not mention a battery issue.

Here are some stupid questions.... since bobterry suggested "viewing actual values of the passenger SAM" .... where is the passenger SAM located on the R230?
Also, should i monitor actual values with STAR or is there a better way to do it with a volt meter?
What values am i looking for... what is normal and what is not?

Frankly.... that 14.6V i see at the front battery with the car idling....bothers me. Perhaps a new voltage regulator is the right thing to start with....given a new Bosch unit is $40 or less.


Thanks!

bobterry99

No, and you can satisfy yourself that I am correct with the following experiment: Disconnect the rear battery and start the engine. Do you get a red error message?

If you are not getting this message now, you can be confident there is nothing wrong with your rear battery.

The passenger SAM is located in the left-rear engine compartment under the fuse block. I believe the status of Circuit 61 should be "ON". Initially you aren't concerned about the actual status of Circuit 61 but are more interested in what the passenger SAM is determining.

A new voltage regulator will change nothing, since the starter battery is charged by the vehicle supply module.

While the charging voltage on the rear battery is constant, the average voltage on the starter battery varies. I spot-checked mine and measured 14.5 volts. It's my guess that 14.6 volts may not be abnormal; and if it is, the only detriment is a false B1828 code and fault indication in the cluster.

danmm7

So just to be clear..... IF, the voltage on the starting (front) battery is too high, lets say it's 14.6-14.7V .... isn't this voltage determined by the voltage regulator on the alternator?

I've been doing a lot of reading and all documentations states that a RED battery light on the dash is usually related to some sort of starter/front battery issue. Since my battery seems to be healthy and i am seeing this "kind of" high voltage ... i am trying to pin point what else around the front battery may be wrong.
I am eliminating the rear/trunk battery from the suspected items.

Also ... based on the pdf document shared in this discussion, it sounds like the red light will not disappear on its own and it needs to be reset every time. In other words, now i am thinking, my issue may not be constant. It may be something that triggered the light 2 weeks ago, and since i have not reset it, it stays on every time i drive the car. Is this really the case or this red light should go away on its own, if the fault disappears?

SLcharge

The CTEK test showed that the rear battery is taking charge.

Your test with Voltmeter, show that charging voltage of 14.25V at the rear battery is right, but the battery is not taking charge.

I suspect that you have a partly faulty rectifying bridge so that you are getting too much AC instead of DC to the battery.
Try set the Voltmeter to AC and measure voltage at idle. AC should not be more than 0.5V.

bobterry99

No! Refer to my prior post.

Perhaps, but in that case wouldn't you expect the fault code to indicate a defective starter battery? I would.

Don't lose sight of what the B1828 fault code is indicating.

danmm7

I decided to play with the car and my STAR this morning.

Went in the garage and first thing i did was check the voltage at each battery. The car has been parked for almost 48hrs now. CTEK charger has been disconnected since yesterday morning.

This is what the voltmeter showed me:
Rear battery - 12.3V
Front battery - 12.7V

I started the car and surprise! .... NO Red light error. I turned engine off....started it 2-3 more times.....still NO Red battery light on the dash. Like it never happened!
At idle...
the front battery shows: 14.60-14.75V
the read battery shows: 14.22-14.25V

So, what changed that caused the Red warning light to go away?

The only thing i did in the last 48hrs was the CTEK connected overnight on Saturday to fully charge the rear battery. Before CTEK it was at 11.7V ....this morning it was at 12.3V.
Yet, we determined that the rear battery has nothing to do with the Red battery warning light. I am confused, to say the least.

Then i connected STAR to the car and checked some values.

The error code was still stored, even though i was not getting the dash light. I cleared the code.

The Pass-Side SAM shows the following values:

Terminal 30 - 14.3V
Terminal 61 - ON
Terminal 15 - 14.4V

The BNS module values are these:

Terminal 30 - 14.2V
Terminal 30a - 14.6V

I did a terminal 61 check and it passed, as expected. With engine OFF .... Term 61 should be OFF. With Engine ON.... Term 61 should be ON.


Any ideas, based on all of the above?

I realize that i now do NOT have the error light on my dash, so everything is expected to be in range. If i get the red light again... i would have to recheck these values again.
Something is 'acting' up for sure, i just can't pin point it.

whoover

Don't mean to beat a dead horse, but since the only thing that has changed is going from a discharged aux battery to a charged aux battery seems to mean that just maybe the rear battery has something to do with the error.

You should continue to monitor the voltage of the aux battery. 12.3 is still marginal, but much better than the 11.93.

I would advise putting the CTEK back on it for up to 48 hours. Depending on the CTEK model you have, it should indicate that the battery is fully charged and the charger has entered the float mode. At that point, the voltage should be 13.6V. When you disconnect the CTEK, it should drop to around 13.0. If the CTEK can't get above 12.4 or so, the battery is bad. I really don't want to debate whether a bad aux battery can trigger this error. (If you recall, my position is that low voltage to the battery control module can raise spurious errors, but if you don't agree that's fine.) But, regardless of any other problem, If 48 hours on the CTEK doesn't reach float at 13.6 V, the battery is bad and should be replaced anyway.

Also, check that the cables are free of corrosion and tight. If the CTEK fully charges the battery with enough time (remember 13.6 V is the float level of an AGM battery) but it drop below 12.4 when the CTEK is removed, there is a charging problem. The fact that you see 14+V when the engine is on is a good sign, but doesn't eliminate a charging problem. You can have adequate charging voltage but not enough current (amps), due to any number of problems. But a wiring problem (a loose cable somewhere, for instance) is high on the list. You'd see adequate voltage but the high resistance of the loose or corroded connection will limit the current flow.

In summary, hang the CTEK on the rear battery again for up to 48 hours. If it gets to 13.6, disconnect the CTEK and monitor the voltage for a week. If it doesn't, you need to bite the bullet and replace the battery. Maybe not at Autozone?

bobterry99

The K57 relay is powered by the starter battery and is normally electrically isolated from the rear battery. The notion that the rear battery can cause a B1828 fault is implausible.

It's apparent that your power supply module has an intermittent electrical problem or its electrical connector(s) are corroded. I'd check the connectors.

danmm7

When you say "power supply module", are you referring to the BNS module in the trunk, where the K57 relay is plugged in?

danmm7

whoover .... at this point, i am willing to try and explore anything to get to the bottom of this. It's not that i disagree with you, i am just going by the documentation that Mercedes provided and how the red warning light is always associated with some sort of front battery failure/issue. The error code also does not mention about the trunk battery. But.... with these complex cars, anything can be possible, i guess.
I fully agree with you - the ONLY thing that changed in the last 48 hrs to trigger the red light going off....is the rear battery sitting on the CTEK for 12 hours.
I will plug the charger tonight and leave it connected for couple of days, just as you suggested. I will monitor the voltage levels and report back.
Thank you!

bobterry99

Yes.

I'll revise my prior post suggesting the problem is at the power supply module to add that I suppose it could be the passenger SAM as well failing to register Circuit 61.

It's peculiar to me how two very different fault conditions -- a faulty K57, the alternator not charging -- are assigned a common code in the power supply module.

alk247

If they only sense voltage downstream of K57, then it is impossible to tell two failure modes apart.

bobterry99

There are two conceivable tests for K57 done by briefly energizing it: (1) measure the resistance of its coil, which should be around 3 ohms, and (2) verify that its contacts close. I presume "no Circuit 61" means its status received over the CAN is "off" or there is no communication with the passenger SAM.