jtb33

I've got an 07 GL450 with 215K miles. It has had been a solid car with really no problems or issues since I've owned it (bought it at 180K miles) other than me replacing the front airbags with Arnott's. The previous owner took really good care of it. Has zero leaks.

However, last week it started doing something odd. When driving at about 45 MPH, ALL the dash lights flashed (and I do mean ALL - seatbelt light, etc - all of them), the car beeped and it auto-applied the brakes for a second. Within 2 seconds, all the dash lights cleared and it drove fine for the remainder of the 10 minute trip. When I got home, I looked it up and saw many posts saying that was the pre-collision assist and that it would happen on occasion and not to worry about it, so I disregarded it. This week, it started doing that again, but more often. It now happens about 75% of the time I drive it and along with it, the CEL popped on and the car started running very rough - felt like a misfire. I plugged in my OBDII and pulled the codes:

Great. I got home, turned it off and the next morning, started it up, but the CEL was gone and it was running just fine - wasn't running rough, no issues. It drove fine that whole day.

The following day, the same thing happened with the pre-collision thing, the dash lights and the beep, then the CEL and engine running rough. When I got home, I pulled the codes again, but this time they were different:

Completely different - even a different cylinder on the misfire.

Is my PCM going bad? Something else? Admittedly, I did bypass an O2 sensor about a year ago because the cats are pretty much dead due to mileage, but haven't had an issue with that.

Thoughts on what this might be?

Max Blast

My first thoughts for electrical weirdery is a water submerged front or rear SAM. I know you said no leaks, but these cars have a propensity to gather water leaks in the areas where sensitive electronic modules live. Check under both front seat wells under the carpet and on the rear spare tire well for signs of water.

jtb33

Thanks for the reply. I'm stumped by the issues...

I'll double-check today on what you suggest just to confirm, but this SUV hasn't seen any rain or water in 6 months (we live in AZ and it's garage-parked as I work from home).

Max Blast

As far as the codes you listed you need to run a Mercedes specific code reader on it.

eric_in_sd

Possibly loose connection on front fuse block. Mine had to be replaced at a young age. A hodgepodge of codes would, to me, point to flakiness in the ECU. Now, the ECU tends to be binary in its dysfunction. Mostly, people lose one of the driver chips, and then a permanent misfire code emerges.

Learn to capture those codes and then clear them. You don't know if they are new recurrence or just the old code.

Separately, how did you bypass the cat oxy sensors?

eric_in_sd

Isn't the rear SAM in the passenger side rear fender well?

jtb33

10-4. Here are the results:

Note that it pulled up 5, but only 2 of them are current - the two cylinder misfire's:



I pulled up the 4 'pages' in each of those two DTC's and posted the pics here: https://flic.kr/s/aHBqjA53f6

That also includes a new scan of OBDII data, which validated that only the two misfire DTC's are current. Those pictures are included in the above link as well.

Noted. The codes I pulled above were "current" per the reader. There were a few that were old that I cleared.

It's a device - I forget the name of them - that's essentially a hollow steel tube that's the same diameter as the O2 sensor that sits between the sensor and the exhaust system and moves the O2 sensor further away from the exhaust, presumably so it doesn't recognize that more is getting through the dying cats. I'm not about to spend the $$$$ to replace cats on a 15 year old car with 215K miles, so this was a workaround. They make them in various lengths and shapes, as it's a trial and error to find one that's far enough away to get some readings (not too far to not get ANY readings), but not close enough to get ALL of the pollutants.

Max Blast

A hodgepodge of random codes as read by a MB star scanner usually indicates a failing battery by indicating low voltage events. That is if there isn’t water damage to the electronics under the seats and in the rear spare tire well, but you’ll see the same low voltage / ground fault codes for that situation as well.

Your generic code reader isn’t smart enough to figure out those codes.

eric_in_sd

Good point. What is the first thing a doctor does when you go in complaining of some issue? He takes your blood pressure, heart rate, and so on. Do basic diagnostics first. You may have an alternator with jumpy voltage, which the battery might not buffer adequately, which would cause a hodgepodge of ailments. Doc, my foot hurts, and I am blind in one eye. Turns out you have high blood pressure.

eric_in_sd

The point is to note the codes and then clear all of them. If the event repeats, take a look at the codes after.

Max is right; you ought to have a good tool if you are interested in keeping this thing and working on it yourself, which is pretty much a must if you want to keep it - otherwise you will go broke in no time. MBII is a good read-only tool, while the Autel MP808 allows you to write data and control things via the OBD port. A full STAR system can be nerve wracking to obtain, but those successful with it swear by it.

For now, check that voltage with the motor running. If it is not high (14.3V) and steady, you probably need to change the alternator. If you do that, check and probably change the battery as well. They tend to drag each other down. When that is done, look into changing the starter also, as long cranks drag down the battery, which drags down the alternator ... need to keep on top of all three together. This vintage GL also has an issue with poor connection on the primary cable at the alternator. You can see my post on a cheap-ish fix for that.

It would be odd for this to be the only symptom of a failing SAM, but we learn to expect the odd.

Also prepare to check the engine compartment fuse block. Like I said they have been known to cause catastrophic failure.

What adapter did you get for the cat oxy sensor? I don't get how those things work, except maybe that they stop the signal from bouncing around as much.

Prince Somorin

Sorry to go Off Topic slightly but did I just read "Auto Applied Brakes?" Our truck does this?

Thanks.

Brocktoon

I have had a '08 GL diesel since new and this definitely sounds like an voltage problem. Back in the day this was happening to diesels and the fix was the glow plug relay. I guess there was a bad batch or something causing weird voltages, like even when not operational. Obviously a 450 doesn't have any glow plugs, but the symptoms are similar, so I'd agree that I'd look at the charging system first.

jtb33

The alternator seems to be working. Battery voltage while running is about 13.5 with A/C and accessories turned on.

I erased all the codes and drove the truck and the cylinder 8 misfire came back almost immediately. As a potential quick and easy job, I replaced the cylinder 8 spark plug and top coil, but it had no effect, unfortunately.

Will have to look deeper on this. Ugh.

jtb33

Almost every time I start the car, the CEL is gone and the SUV drives butter-smooth for a while; 5 or 10 mins before it does that emergency braking thing and all dash lights come on for 2 seconds. Then the CEL goes on and it runs rough.

Tonight, I took the car to one of the gas station car washes - car has been super dirty for ~6 months now. I've now driven it for an hour since the wash, including on the freeway and it hasn't done the emergency braking thing and the engine has been running really smoothly with no CEL on.

Very perplexing...

Max Blast

The “emergency braking thing” is related to your ESP and SRS codes, but your scanner isn’t telling the whole story. Behind those two codes could be a simple wheel speed sensor or something more complex like a sensor feeding the Pre-Safe system malfunctioning. Since you’ve had voltage spikes and troughs my money is one one or more burnt and failing wheel speed sensors. You really ought to get an MB specific read out of this car, a generic reader is going to lie to you more than it’ll tell you the ground truth.

eric_in_sd

Can't say for sure this is root cause, but 13.5V is low. Possibly when the alternator is failing, the voltage becomes spikey, which you would not see on a meter. It is plenty to keep the battery charged, but the spikes and dips might disrupt the computers.

Change the alternator, and when the new one is installed, check the voltage from the alternator lug to the firewall terminal. If that is not very near zero, the primary cable.

If you don't want to unhook the battery, you can disconnect the primary cable at the firewall terminal. That way the computers will remain powered on and you won't have to reset the power windows etc. Verify there is no voltage at the alternator primary.

eric_in_sd

ABS?

jtb33

Typo - it was actually 13.8v... which is still on the low end, but that was with a lot of accessories (DRL, radio, phone charging, etc), including AC turned on.

Also, just changing an alternator out is 10 times the cost and effort (literally) of changing the spark plug and top coil. Not sure I'm ready to drop $400+ on "it could be this thing".

eric_in_sd

Suit yourself. We're just trying to help you, not make you do dumb stuff.

How much effort (literally) are you putting into diagnosing the problem?

You have marginal alternator output. Radio and phone are negligible. Don't know what you mean by DRL; you mean low beams? If so, that is 4% of the max alternator output. AC only uses power to the extent the cooling fan is running on high. If the alternator has not already been changed, it is well overdue.

MB builds fragile electrical systems. What you have sounds like an intermittent electrical issue. Usually the most efficient cure approach is to fix everything that might possibly be related to the problem first. You don't know that the alternator is the cause, but you do know that it could be the cause, and the alternator will have to be replaced sooner or later anyway, so the logical step is to get everything related up to ideal operating condition. It could also be that your battery is dragging down the alternator; pull the battery and take it to Autozone or wherever and ask them to test it. Or spend fifteen bucks on a load tester tool and do it yourself.

Do your best to get the service records, so you can intelligently answer questions like when the alternator was last replaced.

The lesson: Cars are not like the Pyramids. They are not built of a bunch of components that each will last essentially forever. The only forever part is the body. Almost everything else wears out, so it is not like you are throwing away a perfectly good alternator; you are throwing out one which has had some of its value consumed (and from the voltage, a fair amount). You have a 220,000 mile, fifteen year old vehicle, many of the parts on which are nearing the end of their useful life. A steady drip of parts replacement is in your future, like it or not.

jtb33

Whoa there... I'm not shunning help - I appreciate all the feedback and thoughts, but my point was that several components and systems have been brought up in this thread as being the potential culprit, and if I were to just replace them all based on "it could be that", I'd be spending thousands of $$ playing whack-a-mole. I'd like to avoid that to the extent possible.

You're acting like I haven't replaced anything since new on this 220K mile 2007 GL450. Nothing could be further from the truth and if my initial post suggested that was the case, my fault for wording it poorly. It has had a lot of typical maintenance done at correct intervals. Even the transmission has been rebuilt by a specialty MBZ transmission shop at around 160K miles. When I said it has had no real issues or problems, I didn't mean to suggest that nothing has been done on this SUV. I religiously change my own oil and filters every 5K miles, I've changed the brakes, I've performed regular maint on it along the way. The only 'unexpected' failure, was of the front airbags, which I replaced myself with Arnott's. The starter and alternator are not original - they've been replaced at around 160K miles, presumably with the transmission work. There are no secondary tell-tale signs of a failing alternator either - lights shut off, engine stalls, battery depletion... I'll check the voltage on it again without any accessories on, but I'd be surprised if it weren't mid-14's.

It makes sense to use a MBZ specific scanner tool, but those in and of themselves seem to be around $600 or more, unless I'm not looking in the right places.

eric_in_sd

And I'm telling you these things have finicky electrical systems. You can't just look at the voltage with a meter and assume that because it is >12.6 that means everything is okay. You can't just say oh well the battery is charging and the little red light hasn't come on, so the alternator is fine. The resident expert, who regrettably does not haunt this forum anymore, would tell you to get a new battery and alternator in that thing before doing anything else. You are presumably chasing an intermittent electrical fault, and will go insane until you have ruled out certain common culprits.

Even if a terrific alternator was installed, you are one third the way through its life. If you look at the records you might find whether they installed a rebuilt or new, and if new, whether it was Bosch or Chinesium. When you check the voltage, report on where you put the probe leads. I gave you hints about that earlier.

Also test the battery.

It is great fun to speculate tops-down, but you really have to roll up your sleeves and start doing basic diagnostics. My truck was stuck (and I spent $1300 on unnecessary parts) until I put a borescope in the cylinders and discovered carbon on the underside of the intake valves. If I had done more basic diagnostic work I would at least have saved myself an engine computer and a throttle body, but lesson learned.

I told you about three generally accepted scan tools. There are others. If you cannot afford a $800 Autel MP808, get the MBII. If you cannot figure out what its price is, I hate to inform you but you have a long road ahead of you.

P.S. The 0308 etc misfire errors are usually assumed to be a coil, but it only means that the crank slowed when cylinder 8 was supposed to be making power. So it could be a fuel injector or intake valves; or the coil or spark plug, or it could be the ECU drawing down the voltage supply when it came time to fire cylinder 8. I don't know how many revolutions it has to get the error to indicate it. If it elevates to permanent, so it would light the CEL, it will shut off the fuel injector, so it doesn't "damages TWC" aka the catalytic converter.

Max Blast

Go get somebody with an MB star tool to run a alternator output diagnostic and put this issue to bed already. Measuring voltage at idle will tell you one thing but an actual load check will tell you another.

You already have other things going on with your ESP namely the grabby brakes which isn’t normal, and the root cause of this I think is low-voltage events caused by a failing voltage regulator

eric_in_sd

or one of the brushes in the alternator is getting flaky (literally) and causing inverse voltage spikes ... ?

eric_in_sd

By the way, the implausible engine off time error also sounds like something due to a flaky voltage supply on the ECU.

Possibly also connected, the ECU takes on the job of firing the coils itself. Many coils have driver circuits inside them, so the ECU just sends a signal to the coil, but in this case the ECU provides the current. This places a burden on the ECU, which has to use its precious supply voltage to drive the coils. Thus the 0308 could have been a mis-spark, but no fault of the coil pack or spark plug, and could as well point to a weak and fluctuating voltage supply.

jtb33

Haven't had time to further diagnose things, but following on, the misfire codes have not returned and engine is running smoothly. It runs fine until the emergency breaking and dash lights flick on - which still happens about 5 minutes after starting up the car and driving. This time, after that happened, the CEL turned on and the ESP light illuminated and remained on. I pulled codes via Torque out of curiosity since the car was driving normally; no issues with cylinder misfires were apparent. Codes were:

Current Fault Log
------------------
ECU reports no current faults

Pending Fault Log
------------------
P0335: Crankshaft Position Sensor A Circuit
P2610: M/PCM Internal Engine Off Timer Performance


Going to try to find time to look at it this weekend. No idea though, where to find someone with a STAR system (outside of a MBZ dealership, which I'd like to avoid).