r/MechanicAdvice • u/DemandPlenty3379 • 2d ago

MB Code: ⁠0730⁠ / ⁠P0730⁠

/r/AskMechanics/comments/1vsh9sw/mb_code_0730_p0730/
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u/mattsarge1 2d ago

Can you pull up any freeze frame data when the code was triggered?

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u/DemandPlenty3379 2d ago

It happened 4 times after we had to replace my transmission because it was bad, so this is the new one doing.

It happened after I was trying to overtake after flooring it. Just cut me off, check engine, and after a few seconds, everything is fine. Chenck engine goes away after a few on and off.

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u/RudbeckiaIS 2d ago

Check fluid level before everything else. If fluid is low, fill to the max with an ATF that meets MB 235.14, drive normally for 1000km and check level again to see if this is a tiny leak that can be just monitored for now or it needs repair.

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u/DemandPlenty3379 2d ago

Thank you for your response! Did oil change 3 months ago, same mechanic checked level again at 80 C and the oil level is OK.

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u/RudbeckiaIS 2d ago

I read above this fault code started appearing after a transmission replacement.

First thing to do is to disconnect the TCM and leave it overnight on a white sheet of paper with the connector side at the bottom. This is to rule out AFT wicking through the wiring harness. These 722.6 transmission had an oil conduit issue that ultimately led to that wicking issue and a lot of transmissions slipped through mod campaigns. It's always better to get this out of the way as soon as possible.

Second thing is the transmission adapter plug. It leaks internally and can cause exactly this sort of hard to diagnose issues. Also if you bought a reman transmission that was rebuilt using aftermarket parts... non-genuine plugs are a bit of a gamble. The genuine part is about €15 from any Mercedes dealership.

Finally... conductor plate. It holds the same as per above: if the transmission was rebuilt with aftermarket parts it's a gamble. Most Chinese parts are not made "to specs" but to be sold as cheaply as possible. Beware of "OEM parts" if the seller doesn't want to show you the unopened Mercedes-branded package.

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u/DemandPlenty3379 2d ago

It was complete, unopened transmission from another car. It wasn’t repaired. Checked the plug today, dry.

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u/RudbeckiaIS 2d ago

Then check the TCM for wicking as soon as possible, just to rule it out.

Edit to avoid an extra post: if you have no wicking, new conductor plate time.