C1340 - Open circuit in centre diff lock signal (4 Viewers)

[Marshmallow]

Had a flashing check engine light and the two VSC lights come on when I was just pulling out from a camp site earlier this week. I was able to pull into a local Napa auto parts store in the little town of 800 near the provincial park I was camped at and was able to pull a C1340 from the ABS controller.

I ended up just continuing on home, but my gas mileage was horrible so I thought that perhaps the centre diff is locked instead of just a wiring/controller rabbit hole (I'm pretty sure I was getting under 10 mpg towing a 3200ish lb hybrid, but there was also a wicked head wind too, so not completely sure).

I found the factory service manual links and the first thing to check from the diagnostics section is if the differential is free (but no details) - can anyone direct me how to check this first?

I also played with the centre locking button last night and found it does seem to be working (there is a latching sound and a definite wheel hop trying to turn with the diff locked).

I've also noticed an increase in idle/low RPM vibration while in gear.

Any help on troubleshooting would be appreciated, otherwise I'll start working through the diagnostics part of the manual once I've established whether the centre diff is locked or not.

Thanks,

John

 

[Marshmallow]

Monday post weekend bump - can anyone help point me in the right direction on testing the centre diff for locked or not?

Thanks, John

 

[SICARIO]

Does the lights only come on when you have the trailer hooked up? I have a similar problem with mine, due to trailer battery backfeeding.

 

[Marshmallow]

Going off memory, I would say that the check engine light was not flashing when I started the truck up to hit the air conditioning Thursday morning at the campsite, but I don't remember if it was flashing when I backed up to hook up, or if it was flashing when I hopped back in to pull forward off my levelling dunnage (i.e. after the trailer lights were hooked up, I think when I hopped back into pull forward).

It was still flashing Thursday night when I hopped in to try some things out to see if I could diagnose. I'll double check again today to see whether its still on.

I've never had issues with it before, we've been towing for about 4 years with it (and it now has ~200 000 miles, we bought it at 135 000 miles).

 

[084runnerltd]

10mpg while towing 3200lbs sounds good to me.

Just went on a 650 mile road trip towing my bass boat and averaged about 9.5mpg.

(I am fully armored, with lift, 33" tires, front and rear bumpers as well as being fully loaded with a few hundred pounds of gear.....even if you are stock, I don't think 10mpg is abnormal.)

 

[Marshmallow]

Ok, jacked up the front of the vehicle per page TR-50 in the service manual. When I spun the front wheels, they spun opposite of each other, so I crawled under and tried to spin the front drive shaft, its locked up tight. Put the transfer case in neutral and spun the front drive shaft, both wheels turned the same direction. No change when I locked the centre diff, front drive shaft was locked up.

I'm going to do a fluid change (I suspect its never been done, but I'll know as soon as I'm done) and see if that makes a difference, then I'll start testing the electronics - I know its probably mechanical, but I'm holding out hope that its electrical as it looks like there is no spring return, just a flip of the power through the relay/motor to reverse direction on the locking gear.

John

 

[Marshmallow]

Ok, after much testing and head scratching, I'm thinking I might be chasing a ghost with the C-1340 DTC.

I was using the 2004 service manual I found linked here on the site, which was good and bad - good that its so complete (if a little jumbled in how the PDFs are assembled for each section), bad that some of the wiring diagrams are not the same as for a 2001, but generally its the same with some cable connector changes and the diff lock switch is different. I even sprung for a subscription to Alldatadyi today, but found the circuit diagram was missing the diff lock switch wiring that goes into the ABS computer (but the C1340 diagnostic diagram showed it, but not the 4L switch).

I finally found that the locking circuit was working as designed (I chased the voltages through the relay and without the truck running was actually able to hear it click back and forth in the transfer case) which puzzled me why I couldn't tell with the front wheels jacked up off the ground (or, the second method I tried, front and back wheels on the passenger side off the ground) if it was locked or not. After a little more head scratching, I figured out that if the transmission was in park and the back wheels on the ground, of course the front drive shaft couldn't turn. Same with the two passenger wheels in the air, in park and unlocked I could rotate one tire and the other would spin opposite but as soon as I locked the diff I couldn't turn either tire. With that finally figured out, I put the transmission in neutral - now with the diff unlocked, I could spin front or back tires without any impact on the other, with the diff locked, spinning one tire would spin the other the same direction.

With that, today I turned to checking the voltages into the ABS computer to see if they were correct for the diff lock confirmation switch and the 4L switch - both worked fine with the voltages flipping as designed. I pulled the computer out from under the brake pedal and peeled it open to see if there was anything obvious inside that looked amiss - nope, not going to see anything in there with these eyeballs, its quite a complicated device. Plugged it back in and started to wonder whether I could find a local place that does ABS computer repairs as the price of a new unit is heart-stopping.

When I had figured out the other day that the centre diff was in fact not locked, I took it out for a drive to the grocery store pondering why it was not idling properly, and was running rough under 3000 RPM (I had originally thought it was because the centre diff was locked and I was fighting wheel hop) but the more I thought about it the more it felt kinda like a misfire.

Today, I drove down to the parts store and had them plug in their code reader - yep, misfire on cylinder #5, pending misfire on cylinder #8. I had replaced the #5 coil pack about a year and a half ago with a parts store branded unit and its probably given up. I've got another one on order (unfortunately Toyota wants over $200 for a Denso, so I'll install another off brand one and order a spare Denso from Rock Auto). When the parts store guy cleared codes, the stability control lights stayed off.

So next steps - I'm going to replace all the plugs (don't know when the last time they were replaced, at least 60000 miles ago) and the #5 coil pack and monitor how its going.

I'm now pretty sure I know how all the centre diff controls work inside and out, so all is not lost.

John

 

[NolaNomad]

Monday post weekend bump - can anyone help point me in the right direction on testing the centre diff for locked or not?

Thanks, John

Hey John. What was the fix for your C1340 code? I'm having the same issue with my LX 470. Check engine light came on, not blinking. Center diff works fine but does clunk when engaged don't know if that's any relationship. Did you have it diagnosed and fixed or did you figure it out?

 

[Marshmallow]

I think it was actually a phantom code for me - it showed up when I first pulled codes (out in the boonies 3 hours from home) but I didn't have the misfire code which was the real problem so I ended up chasing this down a rabbit hole I didn't need to go down. Once I replaced the coil pack that was shot, I haven't had the check engine light come back on. I also haven't pulled codes since so I'm not sure if the C1340 ever came back. If I get time today I'll plug in my OBD bluetooth module and see if it shows up (not sure if it will with my iPhone app, it was the parts store code reader that I got the code from).

John