Engine light
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Joined: Sep 2011
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99 ml320
Engine light
I am so new to this, so please be kind, I have a 99 ml302.with 145.000 miles. The check engine light went on the o2 sensor were the problem. it indicated the back 2. my husband changed the front and back, new air filter, tune up and new crankshaft sensor. The engine light was rest, but after 2 weeks of driving, the engine light came on again with the same two codes. What else could be causing this? thanks in advance.
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Joined: Oct 2011
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From: Bronx, N.Y.
2002 ML 320 & 2006 ML500
Both codes show that there is a problem with the heater circuit on each of the two rear O2 sensors.
It is doubtful that both sensors failed at the same time, but anything is possible. Fuse #19 supplies voltage to the O2 sensors, so disconnect the connectors to both rear O2 sensors, and with the key in the on position, check to see that you are getting battery voltage to the blue wire in the #1 position on each sensor.
If you are, then replace both rear O2 sensors, if not then you have an intermittent wiring problem. Post back with results.
It is doubtful that both sensors failed at the same time, but anything is possible. Fuse #19 supplies voltage to the O2 sensors, so disconnect the connectors to both rear O2 sensors, and with the key in the on position, check to see that you are getting battery voltage to the blue wire in the #1 position on each sensor.
If you are, then replace both rear O2 sensors, if not then you have an intermittent wiring problem. Post back with results.
Thread Starter
Newbie
Joined: Sep 2011
Posts: 4
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99 ml320
Engine light
Sorry I did not post sooner, computer crashed. I am getting voltage to both sensors. I replaced them and reset the codes. drove for over 40 miles engine light came back on with exact codes. for the same sensors. Is there anything else my husband can do?
Toni
Toni
MBWorld Fanatic!
Joined: Oct 2011
Posts: 7,107
Likes: 765
From: Bronx, N.Y.
2002 ML 320 & 2006 ML500
Then conduct the tests for the heater circuit at the ECM (N3/10), using a Digital Volt/Ohm Meter which also has the capability of reading AMPS. Only disconnect connector B when instructed; all other connectors in place.
To obtain readings, pierce respective wires with small sewing pins. Wires1B and 2B readings are taken at the bottom of the connector as it will be disconnected.
Engine light
