[laksa]

My key will not start the car. It will not turn in the ignition slot at allmbut it locks and unlocks the doors. The problem started today. The car battery was changed mid last year and I put brand new batteries in the key shortly I started having issues to see if it was a key battery problem. It worked the first time with the new batteries and then stopped.

My spare key however Is fully functional.
Please help.

 

[Benzyle]

If your spare key works then the problem is the key.
You could try cleaning the end of the key .
You could also try spraying a small amount of wd40 onto the key's circuit board. Wipe off any excess .
If this doesn't work , you may need a new key.

 

[tony1963tony]

In my experience, you can spray every magic potion on the face of the earth and, in the end, you'll be at the dealer buying a new FOB.

 

[Benzyle]

You are probably right .
Many key failures are caused by the circuit board being affected over the years by humidity / moisture.
WD-40 repels moisture and can restore conductivity , no magic involved.
For zero cost except a few minutes of time , it's worth a try.
As I said , if it doesn't work , a new key may be the only answer.

 

[Iridium_Silver]

The infra-red window is often the cause, needing regular cleaning.
Putting the key electronics inside an aftermarket key case often solves this issue if the window is badly scratched, or damaged.

 

[rudeney]

Note that the battery in the SmartKey fob has nothing to do with its function in the EIS. The battery is only used for the RCL (remote locking) functions. The EIS inductively powers the SmartKey. It's possible that the coil inside the SmartKey has broken. Other had suggested the IR window could be dirty. What I would do is remove the circuit board from the SmartKey's housing to inspect things. To do that, remove the battery carrier and use tweezers of needle-nose pliers to gently pull the circuit board from the housing. With the board out, clean the inside of the housing to make sure there's no debris in the IR lens. Check the coil and other components on the circuit board to make sure nothing looks broken. I once had a key where the coil came loose and I was able to re-solder it and fix it.

 

[laksa]

Really appreciate the responses people. You’re all very supportive and I appreciate it very much. Strangely when I inserted the ‘ faulty’ key into the ignition everything went back to normal. I will have a look at the circuit board Rudeney. Failing that I’ll take it to the MB techs to hear their diagnosis.

 

[koolhandluke]

Timely discussion for me, so I'll share my experience. Main key ceased to unzip the ignition about 3 weeks ago. Disassembled it to discover coil detached from circut board. Spare key suffered the same fate this weekend, thankfully in my driveway. Local locksmith wanted $460 to program a new one. Found a local electronics repair shop to mico solder both of them for $60. I got them back today and all is well. NorthridgeFix in Los Angeles has some YouTube videos of repairs to infared MB keys. His quote was significantly higher, but far less than key replacement. He has mail in service and tests all functions of the fob prior to shipping it back.

 

[nigel slade]

Years ago had problem with CLK key, it turned out to be the ignition switch on the car, the bit you stick the key in and turn.

 

[93SoCal400E]

Easy fix. Good time to update to Chrome keys if still on the black plastic ones.