MAF reading high
#1
07-26-2019, 10:09 PM
MAF reading high
I am chasing a problem with a high MAF reading and would appreciate any ideas on how to diagnose.
2006 XC90 2.5t 210k miles
Previous owner had new Bosch MAF installed last year. I purchased a new Bosch MAF and get the same results, leading me to believe it is not a problem with the sensor.
Codes are either 1210 MAF flow too high or 120C MAF signal too high.
Watching the live MAF values with a computer I see 28-30 kg/hr at idle which seems high from the numbers I've seen others report, like maybe double what others have seen. At full load near redline I see about 630 kg/hr which seems about right for the rated 208 bhp. After a reset, long term fuel trims eventually go high and throw codes after 10-20 miles of driving. After a reset air mass correction factor climbs from 1 to 1.15 after just a few minutes of idling.
I have checked for vacuum and boost leaks and believe everything is tight, confirmed by multiple smoke tests. I also overhauled the PCV system with new parts, cleaned throttle body, replaced intake, exhaust, and turbo gaskets. All good things at this mileage but none seem related to the MAF high value issue.
I have removed the ECM, cleaned the contacts, reseated. Same for the MAF connector. Wiring looks OK at the MAF connector. I cannot find a pinout for the ECM, that would be helpful as I could then test the wring between the MAF connector and the ECM socket. Anyone have even a partial pinout that shows where the MAF wires terminate in the ECM socket? I hate to tear apart the whole harness looking for a wiring issue without testing continuity/resistance first.
Anyone have ideas other than a wiring issue that would cause a high MAF value at idle and/or low loads?
Can anyone confirm that I am correct in thinking the MAF value in the OBDII data is derived solely from the MAF sensor? If I'm wrong and the OBDII MAF value is calculated using inputs from O2, temperature, or other sensors then I would need to open up the scope of diagnostics to other potentially bad sensors or wiring.
2006 XC90 2.5t 210k miles
Previous owner had new Bosch MAF installed last year. I purchased a new Bosch MAF and get the same results, leading me to believe it is not a problem with the sensor.
Codes are either 1210 MAF flow too high or 120C MAF signal too high.
Watching the live MAF values with a computer I see 28-30 kg/hr at idle which seems high from the numbers I've seen others report, like maybe double what others have seen. At full load near redline I see about 630 kg/hr which seems about right for the rated 208 bhp. After a reset, long term fuel trims eventually go high and throw codes after 10-20 miles of driving. After a reset air mass correction factor climbs from 1 to 1.15 after just a few minutes of idling.
I have checked for vacuum and boost leaks and believe everything is tight, confirmed by multiple smoke tests. I also overhauled the PCV system with new parts, cleaned throttle body, replaced intake, exhaust, and turbo gaskets. All good things at this mileage but none seem related to the MAF high value issue.
I have removed the ECM, cleaned the contacts, reseated. Same for the MAF connector. Wiring looks OK at the MAF connector. I cannot find a pinout for the ECM, that would be helpful as I could then test the wring between the MAF connector and the ECM socket. Anyone have even a partial pinout that shows where the MAF wires terminate in the ECM socket? I hate to tear apart the whole harness looking for a wiring issue without testing continuity/resistance first.
Anyone have ideas other than a wiring issue that would cause a high MAF value at idle and/or low loads?
Can anyone confirm that I am correct in thinking the MAF value in the OBDII data is derived solely from the MAF sensor? If I'm wrong and the OBDII MAF value is calculated using inputs from O2, temperature, or other sensors then I would need to open up the scope of diagnostics to other potentially bad sensors or wiring.
#2
07-27-2019, 12:11 PM
Problem found - bad ground
To answer some of my own questions and hopefully help someone out in the future:
The pinout for the MAF connector is:
1: not used
2: battery voltage ~+12-14v
3: ground
4: +5v
5: signal
I checked resistance from pin 3 to one of the nearby chassis ground points and it was about 8 ohms which seemed high. Cut that wire and spliced in a wire to connect pin 3 directly to the chassis ground, resistance less than 1 ohm. Reported MAF at idle is now in the 12-15 kg/hr range depending on whether or not AC compressor is active and transmission is in P or D. So far have driven about 10 miles with no codes, air mass correction factor and all fuel trims stay within a percent or two of 1 which seems healthy. I am pretty sure the bad ground was the culprit.
The pinout for the MAF connector is:
1: not used
2: battery voltage ~+12-14v
3: ground
4: +5v
5: signal
I checked resistance from pin 3 to one of the nearby chassis ground points and it was about 8 ohms which seemed high. Cut that wire and spliced in a wire to connect pin 3 directly to the chassis ground, resistance less than 1 ohm. Reported MAF at idle is now in the 12-15 kg/hr range depending on whether or not AC compressor is active and transmission is in P or D. So far have driven about 10 miles with no codes, air mass correction factor and all fuel trims stay within a percent or two of 1 which seems healthy. I am pretty sure the bad ground was the culprit.
The following users liked this post:
Jeshurun (05-16-2023)
#3
07-27-2019, 12:16 PM
As you may notice I am new to the forum with this thread. I would like to generally thank everyone who participates here, I have found answers to a lot of questions by searching the forums. I imagine there are are many others who find valuable information here yet do not sign up just to post a "thank you."
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