Code 31

[Bob Eyres]

Hey Guys, I'm just waking up the ZR-1 after a long 4 yr. rest

Everything is ok but when I took it out for a run it ran like a bear at first, then popped a service engine light and the Valet mode came on, down on power. After about ten miles of very strong performance it's reading a code 31

Is that a cam sensor like it says in the book, or what?

I've let it cool repeatedly and gone back out. It will seem completely normal for about ten miles of being hammered, then pop, service engine light and code 31`

Any thoughts??

Thanks in advance.

[SAM/CH ZR-1]

Bob
Theoretically it's the cam sensor. How is the condition of your alternator?

[Bob Eyres]

I think the alternator is fine. It's putting out. Fresh battery, fresh fluids, Fresh stainless injectors.
It flies just like it used to, until it warms up. about ten-fifteen minutes of driving then it lights up the engine service light and code 31??

[XfireZ51]

Did you disconnect the BATT and clear the ECM? Do that and see if 31 comes back.

[Bob Eyres]

Originally Posted by XfireZ51

Did you disconnect the BATT and clear the ECM? Do that and see if 31 comes back.

Yes, I did and we tested three times, same scenario.

The cam sensor sure looks like the culprit. I scanned the interwebs and found them available from $180.00 (Rock Auto), to nearly $300.00 for a NOS Delco.

I'm not in the habit of buying $200 parts without knowing for sure whether that will fix the problem, so I decided to pester Marc H for a second opinion.
He ran through some possibilities, mostly electrical, saying that interference from a bad spark plug, or plug wires, or the worst, a problem with the CCU might be at fault. Although I had just put new plugs in (AC Delco) none of those other things seemed to be likely. Mostly because the wiring is in it's usual configuration and not up against, or tangled with the Cam Sensor lead that goes from under the drivers side cylinder head (between the middle two plugs), up to the CCU.
BTW, it's out in the open and looks quite easy to change. Grandma could do it.

Marc agreed that because of the repetitive nature of the problem, (runs great when cold, pops a code and goes to valet power when warmed up), the sensor is most likely to be bad.

A new one is on the way from Rock Auto, and I'll post how this shakes out.

But I'd also like to thank Mr. Haibeck to take time from his busy day to give me his opinion. I'm more than a thousand miles away, and not one of his customers, but he took the time to tell me what he thought. And as we all know, what he knows about the LT5 is pretty damn valuable to all of us.
Thanks, Marc.

[XfireZ51]

Marc is the walking Brittanica of C4 ZR-1s. Now that he owns a C6 ZR, I suspect he'll do the same there.

[RICHARD TILL]

I had the same exact symptoms with a code 31. A sensor solved the problem.

[SAM/CH ZR-1]

A bad going alternator can cause, even before the battery light turn on, some error codes especially during hard driving or accelerating. I noticed that several times by my own and by some customer cars.

After replacing the alternator the code 31 did not show up again.

[Paul Workman]

Originally Posted by SAM/CH ZR-1

A bad going alternator can cause, even before the battery light turn on, some error codes especially during hard driving or accelerating. I noticed that several times by my own and by some customer cars.

After replacing the alternator the code 31 did not show up again.

Thanks! Another item to add to the list of low voltage effects.