Replacing the starter relay
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2010 C 300
Replacing the starter relay
Hey all, quick question - I think my starter relay might be going bad (2010 C300 Sport).
Going to test it first, but supposing it does need replacing, what kind of relay can I put in there? Will a generic 5-pin relay from O'Reilly do the trick? I found this:
https://www.oreillyauto.com/detail/c...r+relay&pos=29
Going to test it first, but supposing it does need replacing, what kind of relay can I put in there? Will a generic 5-pin relay from O'Reilly do the trick? I found this:
https://www.oreillyauto.com/detail/c...r+relay&pos=29
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2010 C 300
@cvx5832
I don't know for sure if it's the relay, but I've noticed some weirdness going on with it, so I want to test it before moving on to other options.
On paper, my issue looks like an ESL failure, but I actually think it's something else. Here's what's going on:
I recently had several major services to the car: new engine installed (pre-owned), new starter, and I had a dealership drain a bunch of water under the floorboards and fix the wiring that had been shorted out.
My guess is it's either a fault with the EIS/DAS (both keys have the same issue, but who knows — maybe both just so happen to have a misaligned IR piece on the circuit board?), or a fault with the starter/starter relay. It could also be some kind of weird electrical anomaly that resulted from the car having been flooded + rewired.
I found this video immensely helpful when trying to address potential ESL failure. It seems like a lot of people immediately assume it's the ESL when it could be any number of things pertaining to the DAS:
I don't know for sure if it's the relay, but I've noticed some weirdness going on with it, so I want to test it before moving on to other options.
On paper, my issue looks like an ESL failure, but I actually think it's something else. Here's what's going on:
- It sometimes takes 10 - 20 minutes for the car to recognize there's a key in the ignition. No ESL motor noise, no dash lights — but I'm also not getting the "take key from ignition" message that is common with an ESL failure.
- On a complete cold start, the car recognizes the key immediately. It only starts acting up when I've been driving for 30 minutes or so.
- When it won't recognize the key, I can often get it to kick in by unplugging/re-plugging the starter relay.
- When I check the engine bay fuse box with the car off, I'm hearing clicking coming from one of the relays (I need to double check which one)
I recently had several major services to the car: new engine installed (pre-owned), new starter, and I had a dealership drain a bunch of water under the floorboards and fix the wiring that had been shorted out.
My guess is it's either a fault with the EIS/DAS (both keys have the same issue, but who knows — maybe both just so happen to have a misaligned IR piece on the circuit board?), or a fault with the starter/starter relay. It could also be some kind of weird electrical anomaly that resulted from the car having been flooded + rewired.
I found this video immensely helpful when trying to address potential ESL failure. It seems like a lot of people immediately assume it's the ESL when it could be any number of things pertaining to the DAS:
Last edited by Ben_prima; Sep 4, 2022 at 11:50 AM.
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2010 C 300
Anyway, as far as the starter relay goes, I found an answer in an Amazon review for a relay:
"This relay is not a Multi Purpose Relay. Even if it is a 5 pins, it is not like the normal 5 pins you are used to. A multi purpose 5 pins will connect pin 30 to pin 87a when power is off and will connect pin 30 to 87 when power is on. But this Mercedes relay connect 30 to pin 87a and 87 at the same time when there is power on 86, 85. Except that they have put a diode between 87a going to 87 and 30."
"This relay is not a Multi Purpose Relay. Even if it is a 5 pins, it is not like the normal 5 pins you are used to. A multi purpose 5 pins will connect pin 30 to pin 87a when power is off and will connect pin 30 to 87 when power is on. But this Mercedes relay connect 30 to pin 87a and 87 at the same time when there is power on 86, 85. Except that they have put a diode between 87a going to 87 and 30."
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2021 GLB250 FWD, 2023 GLA250 FWD, 2013 C250, 2015 GLK350, 2005 ML350SE, 2003 E320
The OE Mercedes relay is $17 at the dealer parts counter and about $13 online. It’s a relatively easy and inexpensive parts swap and will eliminate or confirm the relay as the problem.
Symptoms sound like something in the DAS. You have DAS3. If the relay doesn’t solve the problem, a live data analysis of the starting system may be needed to pinpoint the bad component.
Symptoms sound like something in the DAS. You have DAS3. If the relay doesn’t solve the problem, a live data analysis of the starting system may be needed to pinpoint the bad component.
