Hi all -
Dreaded loss of power steering assist happened on my 2011 Denali Hybrid today (just hit 130k miles). Wife drove it to work just fine this morning but it failed while backing up when she left for lunch at work today with Service Power Steering message on the DIC. Had her unplug the battery for a few minutes then plug it back in and the issue did not clear, but DIC message went away. I got in the truck and turned the wheel a few times in manual steering and the message popped back up. I hooked up my OBD tool and read the C0460 "Steering Position Sensor Malfunction" and C0895 "Device Voltage Malfunction" codes in history. Decided to clear the codes and naturally they went away and haven't come back, but assist is still also gone. Drove the truck home with manual steering, unplugged battery for 2 hrs, re-seated the connector on the steering angle sensor at the bottom of the steering column and plugged back in battery and still no assist, no DTCs returning. The interesting thing is if I have the truck running and I turn the wheel quickly back and forth I hear a low-frequency "zipper" noise. When vehicle off doing the same thing I do not hear the zipper noise so the EPS motor is doing SOMETHING but not providing assist. No fuses blown that I can see, though I haven't been able to find the EPS fuse. When I get the time I will go under the truck and reseat the EPS connectors but my hopes are not high right now.

It's been near 0ºF here the last few nights and not over 15-20ºF during the day. We drove it home from up north yesterday without issues. Took it to the car wash yesterday and no issues immediately after that. I am wondering if something got wet and got into the steering position sensor on the EPS itself.

Any thoughts from the crowd here? Is the C0460 the SAS fault on the steering column or on the EPS underwood unit itself? Critical issue since my wife can't drive any of my manual transmission cars

 

Check for a weak 12V battery. There is also a C0895 code that can be set by the electronic suspension control module, but is also due to low 12V battery voltage.

"The APM may disable the 42-volt conversion if the 12-volt battery has low voltage. The PSCM will set DTC C0895 as a result. Verify that the 12-volt battery is fully charged before diagnosing DTC C0895."
"If there is low voltage on the 42-volt circuit only when turning the steering wheel, the power steering motor is drawing too much current. This condition may set DTC C0895."

 

Good point on the battery. We got a new one probably 3-4 years ago due to no-start issues during cold temperature as well but never lost EPS. It's an AGM battery so I'd hope it hasn't failed by now but the quality of batteries has been bad lately TBH...Hopefully something didn't fry with the 12V control module.

 

So while key in accessory without vehicle running but headlights on…battery warning DIC message comes on after sitting about 2 minutes. By default the voltage measures 11V on the DIC as well even before the warning comes on. Once truck is running the voltage fluctuates between 14 and 15V. I was also able to get the service steering message to come on intermittently if I held the wheel up against where the wheels would just break away without assist (corresponding C0895 at PSCM as well). Put the battery charger on for tonight to see if it wakes it up at all…battery showed <25% after being plugged in a few minutes so I hope we are on to something.

 

Charged the battery overnight and it had good voltage at startup today. Still no assist. Was able to get the C0460 fault to come back today though. I'm not sure if it makes sense to try out a new steering angle sensor (the one mounted on the lower shaft of the steering column) or if this code indicates some other sensor issue within the EPS. I do not have any other stabilitrak or ABS codes popping so I'm concerned it might be a sensor internal to the EPS.

 

Here is a video of the noises coming from the EPS unit. engine off and engine running.


Only concerning noise I hear engine off is what sounds like a bearing squeal. The more consistent gravely noise I’m fairly certain is the freewheeling recirculating ballnut.

Engine on there is the squeal and an odd low frequency zipper noise. You can feel the zipper vibration in the steering wheel as well.

 

mine is having issues as well suspect the power supply it self or the charging system i noted the system voltage being 12.9 when it should be 13.3 at the minimum ..could be a faulty battery as well...


i would check the battery cable and make sure it's correctly seated to the battery posts.... incorrect installed could cause issues it's easy for this to happen because of the shape of some batteries


i going to replace the battery from one from the toyota or Honda dealer same price but way better warranty terms... just hope the motor is not bad it's like 700 for a new one
junk yard like 100$

 

Battery is good - I've done a few charge/restore cycles with it (even though it wasn't too bad before it) and it's showing 12V for a while on DIC when I just go key-on before starting. Out of curiosity I disconnected the 3-phase motor connector from the PSCM. There are zero ohms across each of the 3 phases...I am beginning to think the phases in the stator have shorted together (why I don't know). I found another REPS unit on EBAY, so I will be checking the motor windings on that one and if "good" then I will swap the motors on the unit already in my truck. Fingers crossed this works.

The difference between your issue and mine is that mine is not intermittent at all. Once the assist was lost it has never come back regardless of which battery I've had in the car. I am hoping if my phases are indeed shorted it has not damaged the PSCM, but that might need to be the next thing I replace unfortunately.

 

tried conductivity setting on the muti meter?

 

The resistance between the 3 phases of the motor is expected to be low. See the picture here: https://www.laheatingairconditioning...u-need-to-know
You can see all 3 windings join at the center. Each winding will have a very low resistance.
Is it truly reading 0 ohms or a very low resistance?
tried measuring from each of the phases to chassis ground?