A few weeks ago I changed the starter battery because it was over 4 years old. Then two days ago the key would not turn in the ignition. The steering wheel is not locked and will not lock. The buttons on the key work the locks. Now the driver's window is down, the car is stuck in park and the key won't turn. I am not sure how to diagnose if I have a bad key (only have 1) or another issue. Can anyone help with these symptoms?

How old are the batteries in the Key?

I wouldn't think that would be the issue as the fob works the locks

The battery in the fob has nothing to do with it working in the ignition switch. It's only used for remote locking and KeyLess Go. I suspect it may be time to replace the consumer battery. What's the voltage on it? Oh, and to raise the window, try using the "convenience close" function - point the fob at the IR sensor on the door handle and hold its lock button.

EDIT: and one other thing - I don't believe the R230 has a lock on the steering column. I think that's why the gearshift locks and cannot be shifted out of park manually.

The ignition switch needs power from either the starter or systems battery to operate. You have a new starter battery, and the systems battery is able to operate the locks; so assuming power is okay, then the ignition switch or the key is suspect. If the switch is the problem, Star Diagnosis may be able to identify it, but maybe not.

If you think it's a good idea to have a spare key, this may be the time to purchase one and see if it works the switch. Otherwise I would take the car to the dealer for diagnosis and expect the outcome to be a replacement ignition switch.

I know that the power supply control module can engage the starter battery and consumer battery in parallel to assist when on of them is low. Still, I have seen a low battery cause the EIS to not engage. I'd check voltage on the consumer battery to make sure it's good. If it's too low, it may not even be able to engage the power supply module's switching feature, which would happen when the key is inserted and recognized.

It definitely could be the key itself. Do you have the solid black key? If so, check this: Open it, like you are going to replace its batteries, then use needlenose pliers or tweezers to gently slide the circuit board out. Look inside the housing to make sure there is no debris that could b blocking the IR transmitter lens. Also check the IR LEDs on the end of the circuit board. If you have a loupe or strong magnifier, check the wiring on the small coil on the circuit board - I have seen them break. Also, check the IR lens in the ignition switch for any debris.

Finally, I'd NEVER go without a spare key. Yeah, it's going to cost you $200-$300, but it's worth it for the aggravation of not being able to drive the car. To get a spare, just go to the dealer's parts counter with your proof of ownership (vehicle registration or tag receipt) and ID. Tell them you want to order an "extra" key. It will come pre-programmed and ready to use. There is no need to visit the service department unless you would rather have any missing keys de-activated. In that case, they will determines which key(s) are missing and order a "replacement" key that will automatically deactivate the missing one.

Thank you. I had it towed to the dealer as I didn't want to take a guess with a key. I am hoping they will look at it tomorrow and will advise the outcome.

If you disconnect the consumer battery from your vehicle I think you will find that the key can be inserted and turned in the ignition switch. In fact, it is not recommended, but the engine can be started and the vehicle operated normally albeit with the usual limitations imposed by the power supply module from having insufficient power from the consumer battery.

When I worked at the dealership, dead batteries were a daily occurrence. I know what you are saying is supposed to work, but so many times when an E or SL or other car with two batteries would not start, we'd replace the consumer battery and all was well. What I have found is that when these high-amperage deep-cycle batteries fail, their plates warp and they act like giant resistors. When the single battery in my C240 dies, it ALWAYS reacts by everything working except the ignition switch.

I think the EIS actually has logic in it that will shut off the DAS circuit when voltage is too low in order to prevent damaging the SmartKey. Since the SmartKey is powered inductively by the EIS, and its rolling code gets re-written by the EIS at every use, if there are voltage problems, failure could toast the key. This actually used to happen on the W163 and other older DAS-2 key systems with some frequency.

Regardless of this being true it is generally immaterial in the case of the R230.

Suppose the consumer battery is dead or disconnected. When the key is inserted a hard-wired signal to the power supply module (N82/1) causes it to evaluate the voltages on both the starter and consumer batteries. Provided the starter battery has sufficient charge (> 10.8 volts) N82/1 will energize a relay (K57) that causes the starter battery to power the EIS and nearly all of the vehicle's electrical system. This information is detailed further here.

So, on the R230 the only way the EIS will have inadequate power to function is for both the starter and the consumer battery to be discharged.

I'm going to see what happens on mine with the consumer battery disconnected. But it will be next week - right now it's sitting in the airport parking deck while I get to enjoy Detroit.

Another data point for everyone.

I had a 'click' when I turned the key, and the car would not start. I had placed a Ctek charger on both front and rear batteries, and the voltages looked good at both ends.

However, when I removed the 5 year old front battery (after disconnecting the rear first) it was only at about 8-10 volts during testing with a bad cell. New MB battery from the dealer (only easy place to find an exact fit ~$200), hooked up the front, then rear, and it fired right up.

Moral of the story - the rear battery was feeding to the front, and voltage looked good when connected, but the front battery was way short of starting power when removed from the system for testing.

Don't forget to turn the front wheels lock-to-lock to clear the ESP error, and lower all the windows and hold the switches down, and up, for 5 seconds after disconnecting the rear battery.

I just had a similar issue with my 2003 SL. When I went to start it in the morning, the solenoid would click but no crank. I charged the front battery for a bit and it fired up. I took it for a ride to hopefully charge the cranking battery (I keep a battery tender on the rear full time). While driving, the car just quit and wouldn't crank. I had it towed home and I disconnected the front and charged it. After that it started and displayed the red battery symbol for a while. What confuses me is that it doesn't look like the convenience battery (new BTW) made any attempt to assist in charging. Also, shouldn't the battery tender on the convenience battery help keep the cranking battery charged--or do they connect only with the engine running. I'm assuming the car quit because there wasn't enough juice to keep the ignition going, but then again, is that fed from the cranking battery or the convenience battery.

The batteries are electrically isolated unless they are connected via the K57 relay, and this occurs when the front battery is strong and the rear battery is weak.

Neither. With the engine running the alternator powers the vehicle electrical system, charges the rear battery directly, and charges the front battery through the vehicle power supply module.

Thanks--that helps. One more question concerns why the car quit while driving. It sounds like the alternator should have been able to run the ignition system. When I charged the front battery, the car started right up.

It could be a coincidence that the engine died at a time when the starter battery was discharged. There is simply no way to know.

If the systems (trunk) battery is weak, the starter battery can take over and run the electrics as if it were a one-battery vehicle. However, the reverse is not true, and the only way to start the engine with a weak starter battery is to jump start or perhaps use a booster (questionable).

Turned out the key was bad. Thank you very much for your help!!!

can probably be fixed