1985 C4 Corvette, L98 engine, rebuilt with mild Sig Erson cam the only mods from factory.
I'm getting error code 13 -- Oxygen Sensor Circuit Open or Shorted, after about 5-10 miles of highway driving
The 1226870 ECM had aftermarket eprom from HyperTech, #155 302.
Error Code 13
Replaced the Eprom with 'HLH 3200' code (the recommended stock factory tune)
Still getting Error Code 13
Replaced the O2 sensor with new on from O'Riley
Still getting Error Code 13
Ran a new separate wire direct from the O2 sensor to the ECM, with new contact pin for ECM connector
Still getting Error Code 13
Replaced Eprom with modified HLH 3200_1, which had simple change to fan turn-on temp.
Still getting Error Code 13
Got a replacement 1226870 ECM from ebay.
Replaced its Eprom with HLH 3200 coded Eprom
Still getting Error Code 13.

I'm at a loss - anyone have any ideas?

 

Is the wire color on the replacement O2 sensor the same color as what came off and used to work? My recollection is hazy, but I believe the 85 uses a black wire sensor. The 86-up uses a purple wire sensor. At least 30+ years ago I remember trying to use a purple wire sensor on my friend's 2.8L S-10 because that's what I had in my stuff. It didn't work until we bought a black-wire sensor like the one that came off.

Just an idea.

 

I no longer have the original O2 sensor, so can not report back on wire color.
I'll crawl under the car tomorrow & check wire color & report back.

 

My OO 85 that I know still has its original O2 sensor has a black wire. I just went and looked. (Its on the driver side, in the exhaust manifold just above the flange, facing back. Just open the hood, its not under the car.)
My microfiche shows an AFS-20 for 1985-1987 and an AFS-21 for 1988.
rockauto shows the same AFS-21 for both 85 and 88.
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Normally, the O2 sensor voltage varies up and down between .1 and .9 Volts. Code 13 means that the voltage was steady (between .35 and .55 Volts) for more than one minute and thus that the crossing of .45V (the "middle") has ceased.

One thing you could try:
Jumper ALDL A&B (like you are checking for codes) and go for a drive. The SES light flashes fast (3Hz) for Open Loop, and slow (1Hz) for closed loop. In Closed Loop the light on/off mimics O2 sensor activity. Monitor the SES while your driving for the on/off cycle. As the time approaches for it to set 13 (about 10 minutes?) watch the on/off for any changes. If the on/off appears to 'freeze' or go off, or reverts to fast flash (Open Loop) there's something wrong about the O2 sensor input.

If it operates in closed loop, then freezes after 10 minutes,you've tried everything else, I wonder if you have the wrong O2 sensor? If you have a purple wire sensor, I'd spend $20 and try a black wire, which I think is an AFS-20.

WVZR is better at part numbers and applications than I will ever be. Perhaps he will chime in.

 

Way back when I first got a C4 it started having a code 13. I followed the chart in the factory service manual to the end and that was ecu replacement. I replaced that and all was well.

A FSM is really a great resource if you're going to keep a C4 get one.

 

Checked my O2 sensor & it has black wire. Measured resistance from sensor housing to battery NEG (with DVM) & it read 13.6 Ohms.
Jumpered A-B on ALDL port & drove on highway for~ 25 Min. I got the 'fast flash' for the entire run.
When the car cools down I'm going to run a new separate hard line from sensor housing direct to battery NEG & see what happens.

 

It is not going into Closed Loop.

If you solve why it is not going into Closed Loop, I think you'll solve the Code 13.

 

I just got another Ox Sensor, Bosch, 'Black Wire'. When the outside heat subsides, I will install it & see how that works out

 

Here is a 1226870 schematic. After a new o2 if you still get a 13 check for open or shorted signal wire and o2 ecm ground.

 

That looks like the same schematic as my shop manual.
I've tried everything imaginable & still not working.
I've had it - the car is going on facebook

 

Check the ECM grounds corrosion or bad connections can trigger false O2 sensor codes. Also, test the heater circuit in the O2 sensor if it's a heated one. If all else fails, try a known good ECM from a buddy's car before throwing more parts at it. Wiring gremlins are the worst.

 

what’s on facebook?

 

If the signal wire ohms out you can use a vom to see if the ecm is getting the o2 mv signal and if it’s swinging when warm. If it is you possibly have a bad ecm. Not sure you will get more information on Facebook

 

I believe he means, he is fed up with the car and is going list it for sale on Facebook....

 

Might not be the best for the op to own a older car if frustrated over a simple issue.

 

Yeah, I let my frustration get the best of me - for a while. But I am stubborn.
At some point in this saga I had found that the D6 O2 ground return wire did not have continuity to ground. So I ran external wires from the new O2 sensor to pin D7 on ecm connector, and another wire from D6 on ecm connector (which is the engine ground for the sensor) to battery ground. Still same problem.

Came back & ran a new wire from pin D6 on ecm, to a stud on intake manifold. That was the problem, an open O2 sensor ground return to the ecm.
I can now go down the road & have the control go into closed loop, as it should.
Thanks for the encouragement along the way.