I purchased a 2007 GL450 and on the way home my brother filled it up with regular gas. I thought no big deal I read you can put regular in these things BUT later that evening I accidentally hit the shifter behind the steering wheel and it shifted to D7. The Check Engine (CEL) light immediately came on with the code 0432. The car has been running fine but ever so often my RPMs will be off as if Ive shifted. Yesterday the car wouldn't move like the transmission was slipping or something. I stopped and turned the car off and turned it back on and it worked fine.

I have a icarsoft MBII scanner and in the diagnostics of the ME9.7 6/8 cylinder module I get a code 0946 - The efficiency of the left cat converter is insufficient (function chain) (P0422). Is there a way I can read the live data to tell if I REALLY need a cat?

Does anybody recognize the symptom of my RPMs going so high without actual acceleration?

 

can you ever get a cat code if the CEL light isn't on?

I changed the cat within the last 2 years and now this indy shop is telling me that I am getting the code again.

 

Cat has nothing to do with what’s going on here. Yuh may have a stored cat code because you’re not revving the snot out of the engine from time to time and it doesn’t get hot enough to burn off deposits.

shifting to d7 while driving should not have any adverse effect. D1 on the other hand, you just overrevvwd your engine.

Your slipping problem could be just dirty fluid. When was the tranny serviced last?

 

I get transient 0420 & 0422 errors occasionally. Last time was on my road trip; I stopped at the base of Mt. Whitney to camp, and after letting the truck warm up idling in the morning (it was gutenkalt), those cat efficiency errors popped up. Max Blast is right; cold cats build up deposits and lose efficiency.

By the way, the ECU won't let you downshift into dangerously high revs. Or so I am told.

Definitely do a fluid & filter change on the tranny if it's been a while (40k is max interval). Check the pan bottom; it has a magnet to hold shredded iron.

The CEL comes on when certain OBD errors are stored. This is just a subset of the codes that the ECU is reporting. The CEL is just telling you to investigate.

 

that's good to know...