Still have P1491 code, stumped. Please help

[Ben824]

Ok I have made a couple of posts about this this month trying to figure this out on my 97. Someone also commented and said the 97 won't have a P1491 which is false I checked the 97 FSM and it shows a P1491 code is possible on the 97.

I have replaced:

-Fan relay
-Electric fan
-ECU

I still get the code each time I have fixed something and cleared the code it comes back. This last time I swapped the ECU it took 35 miles before it came back on and I didn't run anything that would make the fan kick on.

THE FAN STILL WORKS! Everything operates exactly as it should which makes this whole situation very confusing. I work at a dealer but in order to have them figure it out, I still have to pay them shop time. I get an amazing discount on shop time and parts but still if I can fix it for less I would rather do that.

 

[Digger87xj]

Just an FYI, starting multiple threads on the same vehicle, with the same problem is frowned upon. keep your old thread going.

That said, I'm the one who said 97 didn't show that code in my repair info, I also stated that it was probable that the repair info I was using was lacking. Which apparently, it is.

I did state this though, aand it still holds true.

The only thing that it monitors is the relay control circuit. so a bad fan will not set the code.

You already replaced the relay, so all you are left with is the wiring between the PDC and the PCM. (I've seen corrosion on the terminals in the PDC)

open the PDC and look at the terminals and wires for corrosion inside.

You will also need a DVOM and check that the relay is getting a full 12v, and do a resistance check on the control wire between the terminal at the relay and the terminal at the PCM.

It is likely that there is a short to ground in that wire (most probable an intermittent short), that is tripping the CEL. If the wire grounds, the fan will turn on when it isn't supposed to. The PCM sees the short and sets the code.

 

[Ben824]

Just an FYI, starting multiple threads on the same vehicle, with the same problem is frowned upon. keep your old thread going.

That said, I'm the one who said 97 didn't show that code in my repair info, I also stated that it was probable that the repair info I was using was lacking. Which apparently, it is.

I did state this though, aand it still holds true.
open the PDC and look at the terminals and wires for corrosion inside.

You will also need a DVOM and check that the relay is getting a full 12v, and do a resistance check on the control wire between the terminal at the relay and the terminal at the PCM.

It is likely that there is a short to ground in that wire (most probable an intermittent short), that is tripping the CEL. If the wire grounds, the fan will turn on when it isn't supposed to. The PCM sees the short and sets the code.

I know I know, I have been here almost as long as you but I realized that the first thread had a poor title and the second one wasn't much better. If I could have deleted them both and had just this one I would have.

I actually had the light go off yesterday but then came back on this morning. I bit the bullet and handed it over to my service department since they have the tools and time to take care of it better than I can. I will post back what it was when they are done.