My '99 ML320 has a reoccurring check engine light. The OBDII indicates 2
codes. These are FUEL TRIM BANK 1, and FUEL TRIM BANK 2. Replacing both O2
sensors downstream of the catalytic converters and erasing the codes has not
helped. The check engine light still comes on after a short time and the
same codes are read by the OBDII. Any ideas on what to do next?
Post your problem at www.mercdesshop.com Shop Forum, Tech Help or the ML
G-Wagen & Unimog area. Gilley might be able to help you :^)
Fuel trim codes, i.e. P0170 and P0173, have NOTHING to do with the O2 sensors.
Depending on which direction the trim has reached its limit, depends on the
problem. If it too lean
and has reached its rich limit, in other words it can no longer richen the
mixture, then you have a
vacuum leak [or a bad air mass sensor]. If it is too rich and has reached its
lean limit, in other
words it can no longer lean the mixture, then you have a leaking pressure
regulator or leaking
injectors [or a bad air mass sensor].
Understanding what the faults mean and how they happen saves a lot of money
instead of using the
Mossberg repair technique [loading up the shotgun with a ton of parts and hoping
one will fix it].
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