If you have closed loop operation and no fault codes on the impulse counter diagnostic connection (should have one with a Ca car). I always look at EHA because the duty-cycle has some programmed functions and you always need to know whta its doing to understand what it says.

For instance: somewhere around 1990 on Ca cars one must enter the diagnostic mode to read proper duty cycle. Try initiating a fault code with a two second grounding of the diagnostic pin (4 I think). If you are of that system, doing this will engage the proper duty cycle you are expecting.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician