W210 Check Engine Light - TPS issue or glow plug?
 

Hi All,

I have a 1996 300D with 137k miles and both my "Check Engine" and "Check Engine Electronics" lights are on the dash.

I pulled the codes and I received the following information:

P0380 - Glow Plug/Heater circuit "A"
P0120 - Throttle/Pedal position sensor/switch "A" circuit

Are these issues related to each other? Any recommendations on what I should test to identify the cause?

I would appreciate any help as this is my first W210 and it seems that it could be several things. The car drives fine and I am wondering if somethings needs to be adjusted in the throttle body.

Could you please share some tests I can conduct and provide guidance? Thanks.

Best Regards,
Louis

You have a bad glow plug. Disconnect connector at glow plug relay and probe each terminal to ground. It wil be intuitively obvious which ones are good. Clear codes after replacing bad gp and you should be fine.

Thanks for the response. If it is a glow plug, why is the other code referring to Throttle position sensor? Is a bad glow plug triggering the second code for the TPS?

Also, would you replace all 6 glow plugs or just the bad one? Thanks.

Diesels don't have throttle bodies.. it'll be obvious which plug is bad. it will read an OL or a high resistance that are different than the rest. Remove the connecter from the relay and check them on the ohm settings on your meter.

after that clear the code and see what happens

It seems like I have to remove the intake manifold to test the glow plugs. Is that correct? I changed the glow plugs on my W123 240D and it was really easy.

I hear so much about these glow plugs seizing in the ports and I am wondering if it is safer to have a German repair shop do it.

Any recommendations?

If you replace,I'd do them all.Soak them good before trying to remove,I read they break easy.Do buy bosch replacements.Autolite glow,and sparkplugs are bad for breaking up.

No, to start check from relay end. Relay is located on fender well behind drivers side headlight. The is an electro mechanical throttle position device. It is located between the brake booster and glow plug relay. It will have a cable and some wiring going to it. I've never seen one go bad.

96E300d here, and I had a code P0120 come up, which seems to be a generic code for a TPS malfunction, but does not mean that the TPS sensor itself is the culprit. After doing some searches, another poster brought up the fact that the TPS is also in a circuit with two other vacuum pressure sensors located on the side of the air filter box. One sensor controls the egr valve, the other the resonance flaps. Also in this vacuum circuit, is that small hose that comes off the intake manifold and feeds into a small black sensor. It seems that all three work in conjunction with one another along with the TPS, and send information to the computer system. In my case, I cleaned off all the electrical connectors at the vacuum pressure sensors, cleared the code, and it has not reappeared. The other thing you should check are all the small vacuum lines that activate the sensors. A leak in one of them could cause a problem. Good luck...
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Hi All,

I am still attempting to resolve a P0120 Throttle Position Sensor code on my 96 300D.

Forum member "pimpernell" mentioned in his last post that there are several sensors in the circuit where the TPS is also located. I am attempting to trace all vacuum lines and sensors.

Does anyone have a diagram they can share of the circuit? It would great be appreciated in diagnosing the problem. Thanks.

Best Regards,
Louis

I don't have a diagram, but two of the sensors with the exact same part number are located on the engine air intake filter box. One small vacuum line goes to the egr valve, the other controls the resonance flaps under the intake manifold. The third sensor is located in the engine compartment on the side of the driver side wheel well hump. It has a small vacuum line attached. I no longer have the car, so all this is coming from my limited memory. Good luck!!!!

Here you go. It's from Mitchell, published 1998.

http://www.peachparts.com/shopforum/...2&d=1549397198

You will get good at removing the intake. Once off, the above glow plug tests will tell which one(s) are open. If this a known, previously good glow plug system that has this emergent code/condition, then good, this forum is a wealth of information to proceed cautiously. If this car/condition is new to you, then inspect closely to see if others have broken (radially sheared) any plugs. If so. the head will likely need to be removed for repair. This is your simplest, but highest risk/impact issue.

Hi All,

Thanks for all your guidance and documentation. I was able to diagnosis the P0120 problem as a bad EGR Vacuum Transducer and sticking Pressure Control Flap Transducer.

I am not able to find these parts for my 96 300D on any parts providers. Do you know the exact part number/name for the EGR Vacuum Transducer and Pressure Control Flap Transducer?

Thanks.

TPS mystery continues...
 

I replaced the bad EGR Vacuum Transducer and sticking Pressure Control Flap Transducer. These parts are both the same with part # A000 545 03 27 and are simply called Pressure Transducer by MB Dealership.

After replacing both parts, I am still getting the P0120 TPS code. I feel that I checked all the vacuum lines and replaced pressure transducers and both intake manifold flaps.

What else should I consider to resolve this mystery? Also, very oddly, immediately after replacing both transducers the external temperature display disappeared from the left side of the instrument cluster display panel and the Windshield Fluid Low indicator appeared even though reservoir is full. Any correlation?

Thanks.

If you have a bad glow plug, your motor will run rough any where from a few seconds to 20 or 30 seconds upon startup in the morning, that is until the cylinder with the bad plug begins firing. You will also get heavy smoke from your exhaust for that period.

I have a '98 e300. Six or eight years ago, a glow plug on that car went bad in February. I waited until the weather was nicer in April to fix it with no adverse affects to the car. I'm pretty sure your car has a block heater; you could probably get rid of some of the rough idle at startup if you used it.

I think you should change all of the glow plugs so that you can wait a few years before you have to do it again. Be sure to use a reamer, and repeat the reaming until you don't have carbon on the reamer.

You should read this Wiki paper; it is helpful. PeachPartsWiki: LightMan's Step by Step Glowplug change

It for later model cars but should offer some help. There are also a number of threads that deal with glow plug replacement.