Limp Mode After Oil Cooler Seals on OM642

If you are experiencing limp mode after replacing the oil cooler seals on your OM642 engine in the Jeep Grand Cherokee CRD, Sprinter Vans or Mercedes BlueTEC models the good news is that it is probably an easy fix.

The ECU will show codes for the MAFs and IAT sensors, potentially more. The first thing to know is that codes that cannot be cleared or reappear immediately even with the engine off are and indication that the sensors are no longer connected.  First, check that all connectors are properly seated – the Mercedes connectors need to be fully seated, and “CLICK” into place, or else they will not get a good signal.

If you are certain the connectors are fully seated then you probably blew the fuse that these sensors all get power from, especially if you did not disconnect the battery before starting the job.

The fuse that powers all these sensors is located in the fusebox under the hood.  It is a 15 AMP fuse located here:

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If you pull that fuse you will see that it has blown – e.g. the wire inside the fuse has broken.

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Get a replacement 15A fuse. DO NOT PUT A HIGHER AMP FUSE IN THAT LOCATION.  Fuse amperage is carefully chosen by the engineers designing the electrical system.  Fuses blow to protect other electrical components.  Putting in a higher amp fuse can expose more expensive components & wires to currents they cannot handle.

  1. […] If you are getting a bunch of air sensor codes that are impossible to clear, you might have blown the fuse that sends power to these sensors.  Check your fuse box for a blown 15A fuse.  See our article about this problem here. […]

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  2. […] After replacing the seals, if you are experiencing a lot of engine codes & limp mode you might have blown a fuse.  Check our our article Limp Mode After Oil Cooler Seals on OM642. […]

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  3. Good info. I just had this done a few weeks ago and had some issues with limp mode on the drive home. I’ll check my fuses tonight. (2010 MB ML350 Bluetec).

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    1. Mike – you’re not alone!!!

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  4. I have limp mode occurring at conditions of idle and when decelerating. usually fine at start up and occurs after I have driven at least 10 mins. Generally goes away after restart. Codes indicate “low boost pressure” and sometimes generic “range performance bank one” . I have the GDE tune done before this started which disables EGR (full closed position) and swirl motor (full open position) so I’m quite sure these are NOT the issue. I changed the electronic throttle body (Which they call the EGR flow control) ; no change….changed the boost pressure sensor on the charge tube and intake sensor on the air box (MAP) cleaned the MAF as well…no change. Changed air filter, checked battery voltage at rest and running. Took apart clips on turbo actuator to check for damaged solder joints or corrosion…nothing; it actuates fine. I had the vehicle smoke tested for pressure leaks…nothing was found. Do I have an intermittent “short to ground” here or something else? The only thing that confuses me is the consistency of when the problem occurs: always at idle or decelerating. If that is electrical why is it so darn consistent?? The local garage gave up and said “maybe it’s your ecu” I don’t think it is. Any help or direction is appreciated at this point. Thanks.

    Chad

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    1. Chad – sounds frustrating. When I was fighting a slow-down/coast limp mode issue last year I ended up needing to replace the turbocharger inlet seal and MAFs. The seal had failed and the MAF was weak so when airflow was low the MAF would read way under expected.

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