QuestionQUESTION: I have a 98 s70 which would start hard and gave a P0102 code. Unplugged the MAF and it runs fine. Purchased a new MAF, measured the output with key on, ~ .2V, barely ran but MAF output looked fine. Reset code, disconnected battery. Tried to run for a while to get the computer to re-learn.
The engine still runs very jerky at light throttle and has trouble starting (usually hot). Cleaned the throttle body, no effect. With the MAF connected it doesn't through any codes now. It seams to run fine with the MAF disconnected. I'm wondering if the issue is associated with the rear O2 sensor that is reported as "0" volts. Both 02 sensors have been replace with new Bosch sensors, the voltage looks correct right at the computer. Even tried another computer with the same results. Had the fuel rail pressure tested and tested for vacuum leaks. The system states that it is running "closed loop with errors". I can occationally see it go into “closed loop on O2 sensor” but doesn’t stay in that mode for long. Question: what conditions might cause the computer to "0" out the rear sensor? What readings should I check (MAF at idle)? Help I'm stuck. Paul
ANSWER: Paul,
Bad wires to the control unit can cause misreasdings. The codes you gave me is what we call a generic one. Try and get the system read with a Volvo scanner as the factory codes are better for diagnosing. I also have always use factory H02S since they are compatible with the rest of the system. There have been quite a few problems with the H02S.
I had a 850 that always had posted MAF codes and found wiring to be at fault.
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QUESTION: I did have a local volvo shop put it on their factory machine and the rear sensor showed the same "0". With the MAF connected it doesn't throw any codes. I have ohmed out the wiring on the O2 sensor right to the computer pins and checks out OK. What should the MAF reading be at idle? Anything else I should measure?
AnswerPaul,
MASS AIR FLOW SENSOR
Resistance between connectors 1 and 4;
Approx 110 Ohms
U = Volts DC
Ubat = Battery Voltage
Ulow = Voltage Close to 0 Volts or is 0 Volts
t = Time in Milliseconds
UAC = Alternating Current in Volts
f = Frequency in Hertz (Hz)
%duty = Duty Cycle (pulse quotient) in percent (%)
Control unit "A" side connector
A4 to A5 Ign on U0.1v - 0.2v idling U0.9v Increases with increasing air mass
A5 to ground U low
No charts available showing comparison while testing with VIDA known good readings.
Try a known good MAF see how that works.
