Hi everyone,
I’m currently working through a poor acceleration issue on my car and replaced the MAF sensor with a known working one. Now I am not sure if I have to reset the ECU so that it relearns the long term fuel trim. There are various posts about this, but none for the 940 series and older. I’m confused since I’m not sure if the ECUs in these older models have volatile memory or just adjust as you drive. I’d love to have some input on this and see what everyone has to say.
Thanks.
Volvo 940 new MAF sensor
UPDATE:
After changing the Air mass meter I was still having problems (at times poor acceleration, 1st cold start it either stalled or got very close to it), so today I decided to reset the ECU and it worked like a charm.
I pulled the number 1 fuse in the fuse box (fuel pump/engine management) for 1 minute and tried to start the car for half a second just to make sure power to it was drained. (Fuse box is located in the center console just in front of the gear shift).
An easier and possibly safer way would be to just pull the battery cables out and touch them together for a minute and perhaps try starting the car to ensure no leftover power; but I didn’t have any of my wrenches handy.
I wanna specify that these older model Volvo ECUs has volatile memory as well and save adaptive fuel trim data. My car is a 940, but I know the exact same thing would apply to a 740 as they are quite similar under the bonnet. I’d imagine it’d be similar for the 240 but I am not sure.
After I plugged the fuse back in, I started the car and followed the procedure posted in the following link and quote (I don’t think it’s necessary but I followed it anyway).
https://volvoforums.com/forum/volvo-s80 ... 1-a-38994/
After changing the Air mass meter I was still having problems (at times poor acceleration, 1st cold start it either stalled or got very close to it), so today I decided to reset the ECU and it worked like a charm.
I pulled the number 1 fuse in the fuse box (fuel pump/engine management) for 1 minute and tried to start the car for half a second just to make sure power to it was drained. (Fuse box is located in the center console just in front of the gear shift).
An easier and possibly safer way would be to just pull the battery cables out and touch them together for a minute and perhaps try starting the car to ensure no leftover power; but I didn’t have any of my wrenches handy.
I wanna specify that these older model Volvo ECUs has volatile memory as well and save adaptive fuel trim data. My car is a 940, but I know the exact same thing would apply to a 740 as they are quite similar under the bonnet. I’d imagine it’d be similar for the 240 but I am not sure.
After I plugged the fuse back in, I started the car and followed the procedure posted in the following link and quote (I don’t think it’s necessary but I followed it anyway).
https://volvoforums.com/forum/volvo-s80 ... 1-a-38994/
This procedure is for an 850 Volvo but the principal remains the same. Again it’s probably not necessary but it didn’t hurt, and seemed to helped my ECU relearn quicker as the idle was a bit rough after reset.Originally Posted by Volvo Adaptation Process
Set parking brake, start engine in P or N. Warm up motor until it reaches normal operating temp or until the cooling fan cycles
Allow to idle for one minute in N, then select D and allow it to idle for one minute.
Accerlerate at normal hrottle position (20-50%) until vehicle shifts into top gear
Cruise at light to medium throttle
Decellerate to a stop, allowing vehicle to downshift and use brakes normally.
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