PCM Not Seeing MAP Output
Thread Starter
Teching In
Joined: May 2006
Posts: 31
Likes: 0
From: Texas
PCM Not Seeing MAP Output Had to do the 2 Bar MAP and OS conversion on my 1998 C5. Used 2 Bar MAP part#12569241 and HPTuners' 2Bar OS. My MAP sensor will not read using the following test method:
Disconnect MAP from intake, but keep it plugged in
Connect HPTuners Scanner to OBD2 port
Connect Mitey Vac to MAP hose barb
Turn ignition key to ON position
Connect and start scanning with HPTuners
Pull vaccum or apply pressure on MAP sensor by pumping Mitey Vac
With multimeter connected to the middle "MAP signal out" wire at splice point between the MAP sensor pigtail and the car's original MAP sensor wiring, the voltage sweeps (0-5v) as I change the MAP sensor pressure with the Mitey Vac. It never registers on the HPTuners scanner. I verified that the sensor has 5v power. I don't know how to test the ground, but at the connection point to the car the MAP seems to be working properly.
Is it possible that my PCM is bad?
What else should I be checking?
Thank you for any help!
Disconnect MAP from intake, but keep it plugged in
Connect HPTuners Scanner to OBD2 port
Connect Mitey Vac to MAP hose barb
Turn ignition key to ON position
Connect and start scanning with HPTuners
Pull vaccum or apply pressure on MAP sensor by pumping Mitey Vac
With multimeter connected to the middle "MAP signal out" wire at splice point between the MAP sensor pigtail and the car's original MAP sensor wiring, the voltage sweeps (0-5v) as I change the MAP sensor pressure with the Mitey Vac. It never registers on the HPTuners scanner. I verified that the sensor has 5v power. I don't know how to test the ground, but at the connection point to the car the MAP seems to be working properly.
Is it possible that my PCM is bad?
What else should I be checking?
Thank you for any help!
Have you tried putting in the stock file and seeing what happens again? There should be a raw voltage signal pid also to watch what it is putting out to make sure it is matching. I doubt it is a bad computer. Make sure there is no issue with the wires going to the front of the car on that harness either by the front passenger side injectors.
The custom multi-bar OSes require that you use the
new (additional) MAP PID, the old one becomes zombie.
Look for it in the list and substitute it for scanning. All
your old configs will be referencing the dead guy.
new (additional) MAP PID, the old one becomes zombie.
Look for it in the list and substitute it for scanning. All
your old configs will be referencing the dead guy.
Thread Starter
Teching In
Joined: May 2006
Posts: 31
Likes: 0
From: Texas
Thank you for the replies.
I have not gone back to the stock OS. Honestly I didn't know I could.
My car is a 1998 so there is no 2bar PID. HPTuners is supposed to just read it under the stock MAP PID. I erased my "vcm scanner.cfg" file and let it reload. During my scanning session the MAP read 65kpa the whole time. Over an hour.
Does anyone see an issue with my test method?
Also, I have tested and verified 5v power at the sensor and a sweeping 0-5v signal on the middle pin. I can not however test the ground.
How do I test the ground?
I have not gone back to the stock OS. Honestly I didn't know I could.
My car is a 1998 so there is no 2bar PID. HPTuners is supposed to just read it under the stock MAP PID. I erased my "vcm scanner.cfg" file and let it reload. During my scanning session the MAP read 65kpa the whole time. Over an hour.
Does anyone see an issue with my test method?
Also, I have tested and verified 5v power at the sensor and a sweeping 0-5v signal on the middle pin. I can not however test the ground.
How do I test the ground?
Thread Starter
Teching In
Joined: May 2006
Posts: 31
Likes: 0
From: Texas
Hello Guys. I did more testing today and verified that I do have MAP voltage at PCM. I found a MAP Voltage PID and reverified after probing the wire at the PCM connector. The MAP PID still doesn't read in the scanner though. If I scan MAP Vaccum it reads, but inversely. Meaning as I increase actual pressure the MAP Vaccum decreases as voltage increases. So wiring is good. [B]Could my OS be corrupt? [B] I havent reverted to the old one yet
