'97 E300D - K40, Ignition, or????
 

All -

I have a '97 E300D with 72K on it. Car was running perfectly, and then randomly started getting the Multifunction screen - ETS, ABS, Brake Lining lights. Sometime can be reset, other times stays on and car goes into limp mode. Sometimes the Check Engine light comes on - in some instances goes back out pretty quickly, and at other times stays on for days.

So I think I am looking at a K40 or Ignition - possibly wiring harness? It's pretty frustrating, since the car is otherwise a pure joy, but at this point I don't want to drive it for fear of where it might leave me!!

Any thoughts or advice is appreciated.

-Reed

Not many harness problems after 95.

By "limp home mode" do you mean trans is in 2nd and reverse only?

All four tires are the same diameter right?

Drive with your CCU set to screen 24 and monitor batt voltage (engine on, press and hold REST for 5 secs, use AUTO buttons to toggle to screen 24); observe while fault occurs, may be low voltage is causing computer to loose communication with brake switch or wheel/trans speed sensors, etc.

TMAllison -

Your description of the "limp-home" mode is accurate, and the tires are all the same size, and pressures are right.

There was a complete battery drain recently - but car seems to have recovered from that alright - could that be a clue?

Also - forgive my ignorance - but what is a CCU?

-Reed

Climate Control Unit on dash.

Ah - interesting - will try that.

Many thanks!!

-r.

BTW - what *should* the reading be?

Thanks again.

-r.

It should be fairly constant, even if it does not exactly represent battery voltage.

I am sure if you go to Autozone to scan the code its going to come up P0600 Serial Communications Link. I have been having this issue on and off now for about a year. I can make mine do it by shutting it down and restarting within one minute. It usually happens when I stop for a drink at the local convenience store. Occasionally it will just come on at highway speed for a few minutes then go out again. Like you my battery was completely drained once, so maybe we are on to something.

So here's what I have found so far -

Check Engine light is currently on.

Prior to starting, reading is between 10.1 and 11.1. After starting, it hovers around 11.5 for a bit, then slowly creeps up to average of about 12.7, ranging from about 11.9 to 13.1.

I shut-off the car and quickly retstarted it, which triggered the ETS-ABS-Brake Wear cycle, and limp mode. When I restarted the car quickly after shuttung it off, reading was back in the low 11s, and then came back up fairly quickly.

I couldn't get it to act up while driving down the road.

Here's what I am wondering, considering this as well as the fact that e300d97 also had the full battery discharge issue and similar symptoms:

1 - What should the pre-start and running readings be? How much should they vary?

2 - Is it possible that something was fried or damaged when the car was jump started (relay, voltage regulator, etc)?

3 - Is it worth replacing the battery at this point? Is there a *better* battery for these cars, considering the apparent sensitivity to voltage fluctuations?

Happened a few times to my wife today, then wouldn't do it for me.

Ugh!

-Reed

With your car running, connect a voltmeter to the battery, or between the battery terminal under the hood and a ground point on the body (not the engine). See how that compares to the reading on the climate-control unit.

Mine always reads about 13.5, but the battery voltage is slightly higher.

Voltage before starting suggests the battery is low, possibly/probably due to the earlier problem. Voltage while the engine is running looks OK, suggests the alternator is OK. These cars are very sensitive to voltage levels and will do strange things (like those you have observed) if the voltage gets too low. The jump starting probably didn't do any harm (but can't be ruled out 100%). There are other things to check first.

Take Matt's suggestion, monitor battery voltage when the engine is running, immediately after shutdown, and the next morning before starting. If the voltage drops significantly overnight and is at or less than 12 volts, you have a weak battery. A good wet lead-acid battery should float at 12.5 volts or more. You can try putting the battery on a trickle charger overnight for several days, see if it recovers. If not, replacement of the battery would be the next option.

Jeremy

Your voltage readings are right on. Similar to mine. Keep in mind that the 96-97 E300's had a slightly lower amperage alternator. It's something silly like a 70 amp or something. The turbo 606's have a 95amp I believe.

However, it would be cheap insurance to replace that K40. About 2 years ago or so I had an episode where I parked the vehicle to run some errands @ a CVS or soemthing. When I got back to the car and tried to start it wouldn't catch. I tried again and it would crank but not catch... I gave it a few minutes, tried again and all was well. I replaced the K40 very soon after as a preventative measure and haven't had a similar occurance since.

The cigarette lighter is a good (+) source.

I'd check your charging system; battery and alt, especially as you had a charging prob previously.

Would be helpful to know what code is present too although will prob point to one of the faults you already know about.

Okay - here's where we are:

1 - After seeing the fluctuations in the battery readings, and thinking ther was a little too much of that - confirmed by a voltmeter - I decided to replace the battery, which was interestingly an MB battery, and for all I know may have been original.

2 - Opened-up the battery compartment (read: pulled the rear seat), and the insulation covering the battery was pulled-back. Clamps on terminals seemed a little bit loose, but nothing catastrophic.. Still...

3 - Replaced battery with the appropriate Interstate (MTP-93, $130) and put it all back together. Reset headrests and windows per instructions in the owners manual.

4 - Car fired right up, CE light still on. Voltage readings seemed steadier. Drove around the block - so far, so good. That was Wednesday evening.

5 - My wife drove the car yesterday - about 60 miles - and after her first drive the CE light went back off (before I was able to go and have someone pull the code).

Since then, no problems. My fingers are crossed. If nothing else, this certainly appears to be *related* to the trouble. Hopefully it is cured. I am knocing on a LOT of wood right now....

Stay tuned!

-Reed