2002 Xterra - Need some help with ABS problem

[red_5]

2002 Xterra, 4x4:

So me ABS light comes on... Then goes off after a couple of drive-cycles... then comes back on and stays on.

I pulled the code with my OTC scan tool and it's telling me "C1111 - ABS Motor".

I've gone through the ABS diagnostic tree in the Nissan service manual for the vehicle, which is very short and has no in-depth procedures/specs for testing individual components tied to ABS the actuator unit, which encompasses the ABS valve body, motor and control module (the control module and motor are bolted to the valve body and removable in a matter of minutes without disturbing the hydraulics). According to the manual, if there are no "faults" in the wiring (open circuits), the connectors are in good shape, there is battery voltage at the specified pins on the vehicle-side ABS controller connector and the ground circuits are complete then the fix is to replace the entire actuator assembly.

There is no mention of any procedures for testing the motor itself or checking output voltage from the ABS controller to the motor itself. I took it upon myself to test these and concluded the following:

Although the polarity on the ABS motor connector on the ABS controller isn't marked, it was easy to determine as there is 0 voltage on either terminal at key-off, but +8.5V on one at key on. No continuity to ground on either one. Extrapolating from this, I determined the + terminal on the ABS motor connector and applied battery voltage to that one, then grounded the other one to chassis ground, which resulted in the motor purring nicely.

Given what I've learned, my best guess at this point is that the ABS controller should either be supplying battery voltage to the motor at key-on and closing the circuit on the ground side when the motor needs to run or 0 volts until the motor needs to run. I can't think of any reason for less than battery voltage to the ABS motor, which implies that the controller has failed.

Since this is a $1200 part and my first hands-on with ABS on this vehicle, I'd appreciate any input from those that have some experience in this area on Nissan vehicles.

Thanks in advance.

 

[red_5]

Update: I solved the problem on my own without buying any parts so I thought I'd share what I did in the event it might save someone else some grief (and $1200).

After thoroughly inspecting all the connectors/wiring and re-testing everything, including removing the electronic module from the actuator assembly and finding zero corrosion or other evidence of naughtiness and no change in the problem or reported trouble code, I had a thought.

I removed the pump motor and operated the pump pistons in the actuator manually to make sure there wasn't anything hung up there (the motor shaft has an eccentric that simply moves the piston assy in the ABS actuator housing back and forth as it spins). I then applied 12v power directly to the motor and let it run for a few minutes thinking that since the truck sits a lot, perhaps the brushes were stuck or the commutator/brush interface was wonky from resting in one position for a long period of time. After I did this, I reinstalled the motor, cleared the fault code with my OTC tool and went for a test drive.

Guess what? No ABS light and the system works normally with ABS fully operational.

It's obvious that the motor itself was the culprit. My best guess is that the brush/commutator interface was either dirty or the brushes were stuck a bit and the first time I put power to the motor it just happened to stop on a funky spot and the controller detected the higher resistance as a faulty pump motor. Running the motor directly for a decent length of time off battery power while I had it off the vehicle was apparently enough to solve the problem.

Thanks R/C car experience for teaching me about electric motors!

 

[bushnut]

good stuff man.
I wonder if this would be useful for the Pathfinder (do they run the same ABS system)?
my ABS light has been turning on and off irregularly for a few weeks now.

 

[red_5]

Can't say for certain, but I'd guess the systems are different as the parts for the Xterra are very year/model/drivetrain/etc specific.

 

[red_5]

And bad news: After 3 1/2 weeks of daily driving and no ABS faults, the problem has arisen again. This time, the fix I mentioned previously did not make it go away. I had to replace the ABS Controller and motor.

 

[mattcooksb]

And the even worse news. The ABS light has been going on and off ever since I picked it up in Chico, but only being on about 5% of the time. It became continuous in Mexico when the pads wore down to the squealers, but returned to it's usual story after a brake job. I'm glad I found this post to know I'm not the only one to deal with this mystery. On a better note, the truck has been flawless otherwise!