Freddydlm

Hi there,

I am relatively new to the forum and have decided to try and maintain my truck on my own instead of spending 300-500 every time I go to the mechanic. My ML500 has 380k miles on it, still runs like a dream, but had the check engine light come on and plugged in the Micro Mechanic in to read what was going on. I am getting the code P0171, P0104, P0422, P0432, and P0404. Also, when I opened the hood it seems that the coolant is bubbling at the connecting point and seems a bit low. Any and all help would be greatly appreciated! Thanks!

khomer2

P0171 System too Lean (Bank 1) ) faulty air mass flow sensor
P0104 Mass or Volume Air Flow Circuit Intermittent

P0422 (main catalyst efficency below threshold bank 1)
P0432 (main catalyst efficency below threshold bank 2)

P0404 EGR issue - Faulty EGR valve / Faulty EGR sensor/ EGR sensor wiring/connector problems / Carbon buildup in EGR valve



For the first 2, could be the MAF. disconnect the MAF for a drive and see if it changes anything. It sets ECU to default setting.
The 2nd two relate to Oxygen sensors - they may be going.
Last one, EGR probably needs to either be replaced or cleaned out.

As to the bubbling coolant, what connection point are you referring to? More info?
Have you got a small leak somewhere. maybe long the edges of the rad?
Inspect the garage floor just below the rad area for signs of a leak. (put down some corrugated cardboard)

Maj. Dundee

Bubbling coolant could be defective coolant cap, defective thermostat, or head gasket which probably explains the bubbling and low coolant level.

Block Tester is the best.