Hi all,

I have a C200 diesel (55 plate), and it's recently had a the MIL come on (orange). I've plugged in the trusty old code reader and it's thrown three codes up. Any help in interpreting would be greatly appreciated. Car seems generally a bit low on power, and was for a while before the lights came on.

Codes are:
P0107 - Manifold absolute pressure/barometric pressure circuit low input
P0472 - Exhaust pressure sensor low
P0698 - Sensor reference voltage "C" circuit low

I can find some info on what the first two relate to, but the third one has me completely foxed. I'm assuming, seeing as they were all there when I plugged in the code reader, that they're all related to the same issue that's triggering the MIL.

It's booked in the dealer for next week, they think it's fine to drive for now and it's the first time they have a loan car. It is occasionally going into limp home mode (rev's limited), but only occasionally. It also has occasionally flashed up on the LCD display a message complaining about an oil pressure sensor error.

Sounds a bit like it's a faulty sensor to me?

Any comments/help greatly appreciated!

 

Did all three codes happen at the same time? It would be unusual for two sensors to fail at the same time. I would look to the cause of P0698. The ECU(ECM) has several 5v (references) outputs that serve a group of sensors. The ECU also provides a stable reference ground(zero volts). The sensor returns a signal on the third wire to the ECU with a signal somewhere between zero and 5v. You should be able to unplug one of these sensors and measure from that connector. Key on, engine not running, one wire should be 5 volts, one should be zero(ground reference), the signal wire may show a tiny residual voltage. The ground is easiest to check. Use a high impedence meter and check for zero ohms to ground. DO NOT use a test lamp. You will be measuring right into the ECU. Ground is probably not your problem but the ECU gets lost if it's unstable. The problem circuit is most likely the 5v reference. Do you get a full 5v at the connector? If yes, the problem is the sensor you unplugged. If no, reconnect this sensor and unplug the other one. Can you find 5 volts? If yes, it is most likely that sensor. If not, the 5 volt wire from the ECU is grounded (or in rare cases open) or the (ouch) ECU is grounded internally. A sharp technician can to wonders with a scanner by comparing the sensor readings. Good luck.

 

Thanks t0213rw.

Yep, all three codes appeared at the same time. I ended up putting it into the dealership for troubleshooting.

They identified the problems as two sensor failures initially. One was a problem with the oil level sensor, which I believe is quite common.

The other was a problem with the air pressure sensor (not the MAF, the one in front of the air filter). They replaced this, but the MIL came back on when I went to pick the car up. Investigating this a bit further and they've identified some worn or frayed wiring leading to that sensor, so it was probably the wiring rather than the sensor. They've fixed that, and I'm off to pick it up this afternoon to find out if that's cured it.

Does it sound sensible to you? And does the P0698 code refer to that sensor - I haven't been able to find any reference anywhere to that code that ties it to a particular sensor.