'97 C230, Fault Code P0170 and Self Adaptation
 

'97 C230, 145K miles, illuminated the CE light approx. 150 miles after routine maintenance, which included new spark plugs (F8DC4), air filter and fuel filter (existing fuel filter was factory original, having never been changed). Vehicle performed well and was free of fault codes prior to service.

Upon inspection, using a M-B HHT, only one fault code was obtained: P0170 - B Self adaptation CTP (idle) at limit (N3/10)

(Note the M-B HHT's description of P0170 is more specific than the published description of " Fuel Trim Malfunction - Bank 1".)


Real time data culled from the ME 2.1 test menu included:

a) Section 01, Check CTP, Exhaust Emission Test: CTP (idle recognition - "On" (test 30)

b) Section 02, Check Engine (page 10): Self adaptation - partial load factor - "1.06" (test 25); and Self adaptation CTP (idle) - "1.000 mg" (test 26).

Other than a lazy oxygen sensor, all other data was within normal limits.

The primary lambda sensor was renewed, as it was factory original and slow to respond. (The MAS was replaced with a new Bosch unit approx. 6 months ago; secondary oxygen sensor was renewed at 90K miles.)

The ME 2.1 fault code was cleared but reappeared after approx. 75 miles. Vehicle runs flawlessly, although a short period of idle roughness was noted each time after the CE light illuminated.

The self adaptation value of 1.06 would indicate a shift toward the lean. In light of the current findings, could this be symptomatic of a failing MAS? If not, what needs to be checked next?

Any truth to the comment that the MASs reman'ed by M-B include a modification that the new Bosch units do not? Or are the failure rates also high for the M-B units?

Yes, the mass air flow sensor is the MOST likely problem. Also the fuel pressure & OR a vacuum leak can cause that problem. FOR that code the mass air sensor will fix 98-99 out of 100.
Don't think there is a "factory" reman for that application. MB part number 000-094-09-48. Bosch # 0 280 217 114/115