Code 13 - 87 SE (Page 1/2)
MERATIME APR 13, 05:05 AM
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).]

olejoedad APR 13, 07:35 AM
The tan wire from the ECM attaches to the block/transmission stud near the starter.

There should be a heavy ground wire from the front passenger side head to the passenger side hinge box deck lid mounting stud.

[This message has been edited by olejoedad (edited 04-13-2025).]

Vintage-Nut APR 13, 10:43 AM
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).]

IMSA GT APR 13, 11:01 AM
Don't know if this helps. Here is the info for the 84 4cyl. Don't know if the grounds are all the same on the 87 but it's a start.

[This message has been edited by IMSA GT (edited 04-13-2025).]

MERATIME APR 13, 02:24 PM
OldJoeDad, Vintage Nut & IMSA GT , Thank you for your input to this code situation. This will help very much. I’ll keep you all posted here.
MERATIME APR 13, 04:15 PM

quote
Originally posted by olejoedad:

The tan wire from the ECM attaches to the block/transmission stud near the starter.

There should be a heavy ground wire from the front passenger side head to the passenger side hinge box deck lid mounting stud.




“There should be a heavy ground wire from the front passenger side head to the passenger side hinge box deck lid mounting stud.”

Is this the ground wire from that stud leading to the trunk lid hinge that you are referring to in the photo below?
olejoedad APR 13, 05:44 PM

quote
Originally posted by MERATIME:


“There should be a heavy ground wire from the front passenger side head to the passenger side hinge box deck lid mounting stud.”

Is this the ground wire from that stud leading to the trunk lid hinge that you are referring to in the photo below?



Yes, it is indeed!
MERATIME APR 13, 11:35 PM
Thank you Olejoedad.
Vintage-Nut APR 14, 08:04 AM
Consider A New Ground Strap from Rodney Dickman:

https://rodneydickman.com/p....php?products_id=485
MERATIME APR 14, 11:18 AM
Thank you Vintage-Nut. 👍