Need help with P1600 Code (1 Viewer)

[BamaHoo]

I need some guidance on troubleshooting a P1600 code on my 2000 LC. Saturday morning I replaced the PCV valve, grommet, ventilation hoses, vacuum hoses, and most of the vapor hoses at the charcoal canister. Was feeling good about it, especially since I was able to retrieve the PCV grommet in two pieces. Left the battery negative off for a while so it would reset the computer and when I started the truck, I had a check engine light. Read the code and it was a P1600 (ECM Battery). Reset it and code came back almost immediately. Runs fine other than now idling higher than it had been (and presumably not saving anything that the ECM “learns” once I turn off the truck).

I’ve read the manual on how to troubleshoot this code, and I’ve tested voltage at the ECM BATT terminal by backprobing it with my VM—no voltage, which I believe means the ECM is likely still good. Just to be certain my backprobe technique was sound I tested two of the ECM’s ignition powered terminals using the same backprobe setup (a straight pin pushed all the way in and then connected to the VM, and for the ground I ran a heavy gauge wire to a good grounding point in the engine bay) and I did get a good voltage reading on the VM with the key “on.” I checked the ECM BATT terminal several times inserting the straight pin in different sides of the wire but never got a voltage to read.

So I think I’m on to the next step which is testing the ECM BATT circuit? I have the immobilizer EFI relay bypass installed with a direct (fused) wire from the battery to the relay, and I have good power to the EFI relay so I guess I’m supposed to test from the fuse box to the ECM? I started to take the fuse box apart but chickened out and decided to post up for some advice first.

Any help/advice would be appreciated.

 

[medtro]

Can you please post picture of your immobilizer EFI relay bypass?

 

[BamaHoo]

Medtro, here’s a photo of it when I first installed it on Feb 11. I can take a better one later today but it’s been working fine since then. After getting

the P1600 Saturday I replaced the Toyota relay with the Bosch one you recommended (had it on hand as a spare) and I also used a small eyeglasses flathead to reach in the relay socket on the fuse box and tighten those female connections and then plugged it all back in. I keep it all tucked in the fuse box in operation and tape the lid down.

 

[BamaHoo]

Medtro, here’s a photo from today:

 

[BamaHoo]

Is it as simple as the fact now that I've bypassed the 20 amp EFI fuse in the fuse box I don't have "always on" power going to the BATT-E9 terminal of the ECM? I'm a novice at reading wiring diagrams so maybe I'm not interpreting it correctly. If that's it, I can't believe it hasn't created an issue until now.

 

[medtro]

Put your EFI fuse back. If that doesn't work, then you need to run fused power to the empty slot of the EFI relay socket.

 

[BamaHoo]

Put your EFI fuse back. If that doesn't work, then you need to run fused power to the empty slot of the EFI relay socket.

Thanks, that's exactly what I was thinking, but I didn't want to do it without another set of eyes looking at it. If I need to run fused power to the empty slot of the EFI relay socket, can I just run it off of the same fused wire as I'm using to power the relay?

 

[medtro]

If I need to run fused power to the empty slot of the EFI relay socket, can I just run it off of the same fused wire as I'm using to power the relay?

Yes

 

[BamaHoo]

For those keeping score, putting a fuse back in the EFI slot solved the CE light/P1600 code, which of course now seems obvious based on the wiring diagram. I'm still wondering why this problem didn't show up sooner, considering that fuse has been out since implementing the relay/immobilizer fix back in February.

 

[cdin]

Hey guys, I’m having a similar issue with a 2001 LC I recently bought.

Yesterday I removed the cruiser's battery and replaced the left headlight. A new code came on P1600 "manufacturer control" came on. I checked ECU voltage is good, then I read this forum and popped the fuse box. I saw the bypass system built from the prior owner to fix immobilizer issues.

Tried clearing OBD but code comes back asap

 

[BamaHoo]

Cdin, are you saying you backprobed the BATT-E9 terminal of the ECM and it shows voltage going to the ECM? If so, I believe that indicates a possible issue with the ECM. Someone else with more expertise can chime in.