Good morning everyone. I have an issue with a Mercedes w245 B-class CDI (euro5 engine).
I have an intermittent check engine light. It comes and after 15 days it could go off by itself. The error is the P040B (generic OBD trouble code) or 169100 trouble code (using an Autel scan with the Mercedes packet reader). It's a code regarding the B16/14 EGT sensor. Essentially, when driving, from diagnosis I read strange values. For example the temp values seems to be stuck around 110 °C, while the other sensors (upstream the turbo and near Kat and DPF) are above 250-300 °C. Sometimes it seems to work fine, reaching values similar to the other ones, sometimes it's stuck at that value I mentioned. The trouble code seems to jump on with cold starts. The Autel reports an anomaly because with cold engine all sensors read ambient temperature but the B16/14 reads higher (for example yesterday it was 185°C with cold engine, other times it's 80°C, etc).
I've heard from a person that he solved the issue after many repairs at the dealer replacing a Z connector (collecting many sensors' ground). But the location of this Z6/85 connector is a nightmare to reach, I think I'd have to remove the entire dashboard, radio, vents, steering wheel, etc.
I'm trying to figure out what is going on. I already replaced the sensor but the problem is still there, sensor was in perfect order (tested with multimeter and heat gun).
If I read voltage at the connector's pin, I read 4.963V. Months ago I supposed it was a fine voltage. But yesterday it came a doubt to my mind. I tested the ground pin and it's at 0.037V with respect to a random metallic part in the engine bay. So the ground wire seems to be not perfectly a ground at 0V.
I'm a novice in eletrical repairs, so I ask you. Is it possibly the cause of the problem? Is it a bad ground?
Then I measured the pin at the expected 5V with respect to the same metallic engine part, and it was 4.99V.
Honestly my first thought was a damage in the CDI ecu internal resistor (I suppose there's a resistor and a voltage divider reading the voltage=temperature), but I don't know what steps to do to diagnose it. Can someone help me?
Other hints: if I detach sensor, diagnosis reads 1200°C. And yesterday it was reading 185°C with cold engine, and detaching and reconnecting the sensor it dropped to 50°C without reason (I only moved wires with hands).
I want to thank you all for help
I have an intermittent check engine light. It comes and after 15 days it could go off by itself. The error is the P040B (generic OBD trouble code) or 169100 trouble code (using an Autel scan with the Mercedes packet reader). It's a code regarding the B16/14 EGT sensor. Essentially, when driving, from diagnosis I read strange values. For example the temp values seems to be stuck around 110 °C, while the other sensors (upstream the turbo and near Kat and DPF) are above 250-300 °C. Sometimes it seems to work fine, reaching values similar to the other ones, sometimes it's stuck at that value I mentioned. The trouble code seems to jump on with cold starts. The Autel reports an anomaly because with cold engine all sensors read ambient temperature but the B16/14 reads higher (for example yesterday it was 185°C with cold engine, other times it's 80°C, etc).
I've heard from a person that he solved the issue after many repairs at the dealer replacing a Z connector (collecting many sensors' ground). But the location of this Z6/85 connector is a nightmare to reach, I think I'd have to remove the entire dashboard, radio, vents, steering wheel, etc.
I'm trying to figure out what is going on. I already replaced the sensor but the problem is still there, sensor was in perfect order (tested with multimeter and heat gun).
If I read voltage at the connector's pin, I read 4.963V. Months ago I supposed it was a fine voltage. But yesterday it came a doubt to my mind. I tested the ground pin and it's at 0.037V with respect to a random metallic part in the engine bay. So the ground wire seems to be not perfectly a ground at 0V.
I'm a novice in eletrical repairs, so I ask you. Is it possibly the cause of the problem? Is it a bad ground?
Then I measured the pin at the expected 5V with respect to the same metallic engine part, and it was 4.99V.
Honestly my first thought was a damage in the CDI ecu internal resistor (I suppose there's a resistor and a voltage divider reading the voltage=temperature), but I don't know what steps to do to diagnose it. Can someone help me?
Other hints: if I detach sensor, diagnosis reads 1200°C. And yesterday it was reading 185°C with cold engine, and detaching and reconnecting the sensor it dropped to 50°C without reason (I only moved wires with hands).
I want to thank you all for help
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