Hello guys and gals I’ve been enjoying this 1987 Fiero SE eversince the alternator situation has been fixed however, about a 1/2 mile heading home yesterday, the vehicle started to have the intermittent check engine light when accelerating. I did a scan and I’m getting a code 13. I double checked the oxygen sensor wire, unplugged it cleaned it, and reconnected it. I’m now having trouble finding the so-called negative ground wire which is a tan wire from the ECM. I also wanted to verify if there is a ground wire from the intake manifold that plays a role with the oxygen sensor? Also, if you all have any other suggestions on what could cause a code 13, that would be greatly appreciate it Thank you.
[This message has been edited by MERATIME (edited 04-13-2025).]
Ground Straps Matters and the Tan O2 ground is particularly picky!
I can't find a 2.5L G503 photo for you...
EDITED I found the service manual location of G503 on a 2.5L on page 8A - 201 - 2 On *This* digital 1987 Pontiac Fiero Service Manual is on page 1035 https://fieroinfo.com/manua...M_Service_Manual.pdf
------------------ Original Owner of a Silver '88 GT Under 'Production Refurbishment' @ 136k Miles
[This message has been edited by Vintage-Nut (edited 04-13-2025).]
Just to reconfirm, is this the G503 connection on the image below? I have found information about the G503 for the 2.8. But I can’t find it for the Iron Duke which mine is equipped with. Thanks.
Hello all ! I am now looking in the engine area of this Fiero SE. I was trying to double check the locations of those negative looped wires mentionedand this is where I found them in this first image below:
My question is if these negative wires in the right location or should they be attached to the bolt below showing in the second image?
Please let me know if what you see on the first image is the correct connection for G503. I couldn’t tell in the service manual on page 8A – 201–2 specifically which exact connecting the negative wires attached to for the location of G503.
Hello all ! I am now looking in the engine area of this Fiero SE. I was trying to double check the locations of those negative looped wires mentionedand.
This is where I found them in this first image below: Note: It seems that these wires were connected to a bolt that attaches the transmission to the engine block. I did not do this. This was how the vehicle was when I got it back after the engine rebuild.
My question is if these negative wires are mounted in the right location or should they be attached to the bolt below showing in the second image?
Please let me know if what you see on the first image is the correct connection for G503. I couldn’t tell in the service manual on page 8A – 201–2 specifically which exact connecting spot the negative wires attached to for the location of G503.
Thank you for your input.
[This message has been edited by MERATIME (edited 04-16-2025).]
As I mentioned, Consider the Engine-to-Chassis Ground Strap Connection in the Path
Measure the Resistance from G503 to three points: *To the Battery *To the Chassis End of the Ground Strap *To the Engine End of the Ground Strap
You want a very low resistance {1Ω to 2Ω} on all the three ground connections; ideally the same value...
Prior to using the Ohmmeter, touch the probes together to measure the parasitic resistance from the leads. Subtract this amount of resistance from the test measurement.
PS - IF after cleaning the grounds and you still have a Code 13, replace the oxygen sensor because you don't have the proper tools to test the unit...
[This message has been edited by Vintage-Nut (edited 04-15-2025).]
As I mentioned, Consider the Engine-to-Chassis Ground Strap Connection in the Path
Measure the Resistance from G503 to three points: *To the Battery *To the Chassis End of the Ground Strap *To the Engine End of the Ground Strap
You want a very low resistance {1Ω to 2Ω} on all the three ground connections; ideally the same value...
Prior to using the Ohmmeter, touch the probes together to measure the parasitic resistance from the leads. Subtract this amount of resistance from the test measurement.
PS - IF after cleaning the grounds and you still have a Code 13, replace the oxygen sensor because you don't have the proper tools to test the unit...
I will test the 3 locations mentioned. I really appreciate your assistance.
