RepairPal is your advocate for car care advice and guidance

Q: check engine light fails to come on. on 2004 Mercedes-Benz C320

during emissions inspection the check engine light failed to come on. What are the possible causes and How can this be fixed.
Get a Repair Estimate
Guaranteed by certified locations nationwide. Learn more
RepairPal estimates are guaranteed at over 1,700 quality certified locations nationwide. Learn more
| |
The ignition switch supplies power to the powertrain computer and the Check Engine Light on the dash, the light should come on when the ignition key is in the on position, if the bulb gets power (and the instrument cluster wiring board is OK) the computer grounds the bulb to turn it on, once the engine starts the computer removes ground to turn off the light and only grounds the wire if it then sees a fault. You would probably be bst locating the computer, and see if that ECU pin is grounding through the ECU and if grounding the pin makes the light work, otherwise you are looking at testing the circuit board or dash bulb.

There is a company that independent auto repair shops get their information from, this same information is available inexpensively for people that work on their own cars.. The information is year make and model specific, covering repair procedures, torque specifications, fluid capacities and specifications, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate
Didn't find what you were looking for?