OV3RTIM3

Ok ive been having some issues with CEL p0178.

1st I bought a brand new flex fuel sensor. That didnt fix the issue.

2nd I bought a brand new pigtail from PointA Engineering.
That didnt fix it either.

I finally grabbed my power probe which i shouldve done from the beginning, and i tested the voltage in the white, pink & black wire. This is the readings i got

Black wire (ground) read 0.0v
Pink wire read 12.2v
White wire read 0.0v and it shouldve gave me somewhere near 5.0v

So i know my issue is with the white wire as to why im getting CEL p0178 for low voltage. Ive been doing some research and ive read that the white wire runs straight to PCM/ECM. Ive been trying to find a pinout diagram for the PCM to see if i can find that white wire to test it for power at the PCM but i havent had any luck in find the diagram.

Would anybody know how i should go about resolving this issue or has anybody had this problem?

tech2

check for an open on the white wire from the sensor connector to the pcm connector c1 pin 56. if the wire is intact and can carry a load, has no short to power or grd...the pcm may be bad

OV3RTIM3

Definetly going to check this out in the morning. Ill keep posting what i find here.

cleveland63b

were you backprobing or checking with it unplugged?

OV3RTIM3

I disconneted the pigtail from the sensor

OV3RTIM3

Ok so i finally got a chance to look more into the problem over the weekend. I disconnected the plugs from the PCM and checked C1 pin 56. There is a break in the circuit between the PCM and the pigtail for the flex fuel sensor. So then i reconnected the C1 plug and stripped the wire and tested it for the 5v signal from C1 pin 56 with the ignition on and the PCM was giving the 5v. So i simply ran a new wire from the ecu down to the sensor, zip tying it along the chassis harness that goes down underneath the truck on the driverside. No more CEL and i was able to pass NYS inspection. Thanks for everyones input, i hope this helps others in the future

Michael Aaron

I'm having the same issue with my pink wire above pigtail. I get 5 volts from white and 0 from pink wire. Anyone have the corresponding pin for pink wire to test pin?

tech2

if the same truck and model year the pink wire is powered by the ecm1 fuse in the underhood fuse block.

Michael Aaron

if the same truck and model year the pink wire is powered by the ecm1 fuse in the underhood fuse block.

I have replaced ecm1 fuse (was blown) got proper voltage on pink and white. Engine turned over and blew the fuse again.

tech2

you will have to get a power distribution wiring diagram. this will show you all the items powered by the ecm1 fuse. once you know them all; you can disconnect them one at a time to isolate the short.