2005 GT MAF 5V Problem

[Laga]

Car was running like shit after trans repair. Had to sit for two months due to family and health problems. Then, Found out both header gaskets were leaking. I could remove top nuts, but can’t work underneath car anymore. Take it to mechanic, he finishes gasket job. In doing so, he swaps upstream O2 sensors. I can fix this with help from kids. Car still runs like shit. Sent datalog to Lito and he says MAF not working. I test everything and find no 5V source going to MAF. All grounds are good. Almost all sensors use a 5V signal from ECM. I test TBPS, and fuel pressure sensor, and they have full 5V. I locate MAF source on pin 25 of bottom ECM connector. I gently clean everything. I have continuity from ECM connector to MAF connector, but no 5V.
It appears that ECM needs repair as pin 25 is dead. Am I missing anything ?

 

[JC SSP]

What codes do you have?

Could something have been damaged (pinched) when tranny was worked on?

 

[Laga]

only codes were for the O2 sensors being switched. No wires have been pinched.

 

[JC SSP]

Ok I had several codes pop up few weeks ago including upper & lower R/L O2 and TPS… turned out to be the TB assembly.

 

[GlassTop09]

Car was running like shit after trans repair. Had to sit for two months due to family and health problems. Then, Found out both header gaskets were leaking. I could remove top nuts, but can’t work underneath car anymore. Take it to mechanic, he finishes gasket job. In doing so, he swaps upstream O2 sensors. I can fix this with help from kids. Car still runs like shit. Sent datalog to Lito and he says MAF not working. I test everything and find no 5V source going to MAF. All grounds are good. Almost all sensors use a 5V signal from ECM. I test TBPS, and fuel pressure sensor, and they have full 5V. I locate MAF source on pin 25 of bottom ECM connector. I gently clean everything. I have continuity from ECM connector to MAF connector, but no 5V.
It appears that ECM needs repair as pin 25 is dead. Am I missing anything ?

View attachment 117562

Laga,
From what you've posted & seeing the wiring labeling, you're pretty much on the right track..................only thing I can't determine is that you've checked pin 25 for the actual 5v+ power off the pin @ ECU board (pin 26 is the signal return.......this is the adjustment to the 5v+ power to the MAF coming back from the MAF after the 12v+ hot wire voltage scaling correction off passing airflow thru MAF slot........this is how the ECU actually measures airmass density thru the change in the 5v+ signal pre MAF vs post MAF........you typed "it appears"......).

Since this 5v+ comes directly off the ECU's onboard transformer (transforms 12v+ to 5v+ to feed all sensors that use this 5v+ power..........) & that 25 pin is tested\verified to be dead, then this pin trace on the ECU board between the transformer & this pin 25 has failed, but the onboard transformer itself hasn't (you've noted that this 5v+ reference is present at all other sensors except the MAF......) thus all other board traces are intact..........soooo, technically, you could tap into 1 of the live 5v+ wires to supply this reference to the MAF off pin 25's wire.......if this doesn't cause other issues w\ voltage offset throwing off the signal return voltage between the 2 sensors being fed from a common power source.......a reason IMHO why the MAF has its own separate 5v+ reference trace off the ECU board.

Otherwise, you're looking at an ECU board repair\replacement if pin 25 is truly dead...........but you also didn't mention that the 12v+ hot wire reference (the part you worked on earlier.......) is working either thus I'll assume that this side is good, yes?

Well, hope this helps you.........not a good situation in either case for a simple solution but it's the best I can provide.

 

[Laga]

Laga,
From what you've posted & seeing the wiring labeling, you're pretty much on the right track..................only thing I can't determine is that you've checked pin 25 for the actual 5v+ power off the pin @ ECU board (pin 26 is the signal return.......this is the adjustment to the 5v+ power to the MAF coming back from the MAF after the 12v+ hot wire voltage scaling correction off passing airflow thru MAF slot........this is how the ECU actually measures airmass density thru the change in the 5v+ signal pre MAF vs post MAF........you typed "it appears"......).

Since this 5v+ comes directly off the ECU's onboard transformer (transforms 12v+ to 5v+ to feed all sensors that use this 5v+ power..........) & that 25 pin is tested\verified to be dead, then this pin trace on the ECU board between the transformer & this pin 25 has failed, but the onboard transformer itself hasn't (you've noted that this 5v+ reference is present at all other sensors except the MAF......) thus all other board traces are intact..........soooo, technically, you could tap into 1 of the live 5v+ wires to supply this reference to the MAF off pin 25's wire.......if this doesn't cause other issues w\ voltage offset throwing off the signal return voltage between the 2 sensors being fed from a common power source.......a reason IMHO why the MAF has its own separate 5v+ reference trace off the ECU board.

Otherwise, you're looking at an ECU board repair\replacement if pin 25 is truly dead...........but you also didn't mention that the 12v+ hot wire reference (the part you worked on earlier.......) is working either thus I'll assume that this side is good, yes?

Well, hope this helps you.........not a good situation in either case for a simple solution but it's the best I can provide.

The only reason I did not test directly off pin 25 was because I wasn’t sure I could safely supply power to the ECM and start poking pins without the connection hooked up. I “front probed “ the ECM connection and checked continuity to the MAF connection. I then hooked all three connections up to ECM and supplied power. Everything worked except 25. I can test 25 directly tomorrow if it’s safe to do so.
Yes, the 12v and all grounds are good.
I should have stated that. Thanks as usual.