HOW TO CHANGE ENCODER MOTOR/SENSOR

bmerr98 · Feb 2, 2015

This is specifically for 2003-2007ish GM trucks with the NP8 electronic shift transfer case, though there may be other applications as well.

Intermittent 4wd operation? Service 4wd message on your DIC? No lights on your selector switch, etc? In the words of slick Willy Clinton, "I feel your pain". Full disclosure - I started to just throw parts at my truck and wasted $50 fast on a new dash switch. Learn from my mistake. Spend $100 or so to get your DTC codes read by a qualified and properly equipped technician. If they come back with a C0327 code (IIRC...), they may offer to replace your Encoder Motor for somewhere around $750, or just the Encoder Motor Sensor Ring for $450 or so.

Goal: TO SAVE YOU MONEY! PUT YOUR WALLET AWAY!!! YOU CAN HANDLE THIS ON YOUR OWN! If yours is like mine, (when it works, it works great), then you know the problem is electrical, not mechanical. That's a good thing.

Skill Level: 3-4 of 10

Time: It took me about 1 1/2 hours including taking pics. I could probably do it again in about half that time.

Special Tools Required: None

Parts: Dorman 600-120 Transfer Case Motor Encoder Ring $39.59 on Amazon
ACDelco 12384990 Transfer Case Four Wheel Drive Actuator Seal $10.27 on Amazon

Or, if you'd rather just replace the whole Encoder Motor
Dorman 600-910 Transfer Case Motor $158.59 on Amazon

Disclaimer: As with any DIY repair, YOU are responsible for your own safety. Neither the author of this article, nor the staff/administrators of SilveradoSierra.com assume any liability for injuries or damages incurred by following these instructions. All reasonable and sensible safety precautions should be taken.

Safely elevate and support your vehicle to give yourself a little room to work. Ramps or jack stands should be sufficient. Set your parking brake.

Your transmission and transfer case should be in Neutral, if possible.

I began by indexing the front drive shaft. Best to keep that where it's supposed to be. Use a spot of paint or white out.

Remove the skid plate from the bottom of the transfer case.

Next remove the band clamp from the output shaft boot and remove the front drive shaft. You may or may not be able to reuse the band clamp. I used a similar sized hose clamp.

Now disconnect the wiring harness to the transfer case. Again, it has the gray lock that pulls straight out, then you can separate the connector.

You should have pretty clear access to the three bolts holding the Encoder Motor to the transfer case. Remove them and pull the Motor away from the transfer case about 3/4" to clear the little drive gear and it should come right out. TA-DA! Your Encoder Motor!

This black water/dust shield should lift straight off. Don't forget it when reassembling!

There are six T-15 Torx screws holding the case together. They are not all the same length, so mind where they go.

The black plastic cover lifts off and with a little persuasion the case should separate.

Don't lose these spacers. They may be sticking to the gear or to the case.

Notice the timing marks on the large gear and the case. In Neutral they should be within half a tooth from each other.

I indexed the gears to each other just in case the smaller gear got moved. Don't let it get moved. I don't know why, but that's what I hear.

The larger gear should lift straight off and the sensor is on the bottom. Disconnect the 3 pronged connector.

This pic isn't great, but you can see scoring from the brushes on the surface of the lands. Out of view is a spot that looked nearly melted from friction.

Installation is the reverse. It only goes together one way (unless hammers are involved), so it's hard to mess this up. Not sure how long the sensors are good for. Mine had been replaced before. I'd have had a couple more pics, but 10 is the limit.

Hope this helps!

Racer_XXX · Feb 8, 2015

Great write up. This will come in handy when I decide to do mine.

airdave · Dec 10, 2015

Thanks for this post! I'm getting ready in a couple day to replace my encoder ring and this write is perfect. If I have anything to add, I'll post a follow-up after I install.
The only things, at this point IMO, missing from your post is: did you place the selector in neutral before beginning this, and was it necessary to replace the seal. I didn't get the seal as it looks like, with care, it could be reused.

bmerr98 · Dec 10, 2015

Yessir! Transmission and Transfer in Neutral (4th line above 1st pic), and the gasket can be reused as long as it is undamaged. I could have reused my old one, but I got the new one not knowing better. $11 later and I know better

airdave · Dec 10, 2015

Oh, my bad! I went ahead and ordered a new seal...rather have it than have to repeat this all over again.

Thanks again!

airdave · Dec 16, 2015

I'm just now changing this out and I'm looking at the gears. You stated that, in neutral (trans and 4wd selector) the timing marks should be within 1/2 tooth of the case timing mark. Mine is 1 1/2 teeth out. This is how I found it when I pulled the case apart. Do I need to do something or just put it all back as I found it?

Thanks, Dave

airdave · Dec 16, 2015

Just got it all back together and it seems to be working fine. 1st time in a long time that I've seen the selector switch go through all the lights, diagnostic when starting, before staying on where I put it - 2wd! I called my local shop that specializes in GM only and asked him about the gear indexing inside the encoder assy. He asked if it was working ok before and I told him yes. He said to just put it back together and it should be fine as the encoder knows where it needs to be and it's not a problem if it's only off 1 1/2 teeth.

Just a little fyi for you guys wanting to do this repair. It's really not that hard but it did take me about 2 hrs. I'm 62 and don't get up off the floor real well anymore. Just be sure you have the proper tools before starting! I used a 15mm socket with a swivel 3" extension for all the bolts. You'll also need a T15 torx bit, and 11mm socket for the u-joint bolts.

Use the above illustration and instructions - EXCELLENT PICTURES AND WRITE UP!

Dave

bmerr98 · Dec 17, 2015

Hey Dave! Just saw your concern about the index marks on the gears and the resolution. I was just passing on what I had read about them, and it seems like it ended up being a non-issue for you. Glad to see the job went well and all seems to be working as it should. It's been almost a year since I changed mine and no issues so far.

Happy motoring, Sir!

airdave · Dec 17, 2015

Thanks. Only thing I'm not real sure of is how to know that 4wd is actually working. I don't know if I can fully rely on the indicator light.

semicrazy · Dec 17, 2015

Great write up.

bmerr98 · Dec 17, 2015

airdave said:
Thanks. Only thing I'm not real sure of is how to know that 4wd is actually working. I don't know if I can fully rely on the indicator light.

Find a gravel lot somewhere, and make a few sharp corners in 2wd. Then put it in 4wd and do some more sharp turns. The difference is night and day. You'll be able to feel the front grabbing and hear the wheels scrubbing in the gravel in 4wd.

You can do this on pavement, but it puts a lot of strain on the drive components since the tires can't slip. If you do it on pavement, don't do it much. Just a little and you'll feel the steering "binding up".

airdave · Dec 17, 2015

Thanks

rexb16a · Dec 21, 2015

Can't thank you enough for this writeup and posting a link to it on my thread to help me solve my issue.

My issue was intermittent. Service 4wd message. Sometimes worked perfectly, sometimes wouldn't do anything and had no lights on the dash switch, sometimes would randomly change position on it's own. Problem first happend once every few months or so then fine the next times I turned off and restarted the truck. Then started doing it every few weeks, then every week, then every day until it was on every time I drove the truck and couldn't do anything with my 4wd system.

I replaced the dash switch-nothing changed. Replaced the transfer case control module and seemed to fix it for about 2 weeks, then back to not working again. This encoder ring did the trick and saved a lot of money over changing the whole motor assembly. If you can get the assemby out, thats the hard part. Changing the encoder ring is really easy, just have to pay attention to gear placement.

Here are a few notes from my experience with the procedure.

Took me about 1 1/2 hrs. Took the 4 bolts out of the u-joint on the front of the front driveshaft and seperated it. Then pulled the factory hose clamp off the rear part of the driveshaft closest to the transfer case. I was able to reuse this one but it wasn't easy to get back on. They must have a special tool from the factory.

The connector plug was a real booger to get loose from the bracket its attached to on the transfer case on my truck cause there isn't a good way to get to it to squeeze the tab and slide it through. The original author of thise writeup removed it from the grey nylon thing now that I look at it. I did the black one where you need to used plyers and squeeze from the backside to release it.

The 3 bolts that hold the encoder motor on had blue locktite on them. Not sure if that was a factory thing but I assume it is considering my truck only has 110k miles. They were very hard to get loose at first until I got past the locktite. Felt like something was wrong but they came out fine.

The tiny torx screws on the encoder motor are different sizes as mentioned in the other post about the procedure. As for mine, there were 2 longest ones on the outside by the tall black tower, 2 medium sized ones on the inside of the tower, and 2 short ones on the other side of the motor.

Couln't get mine switched to nuetral before removing so I just used my wifes white finger nail polish to mark the gears in several placed to make sure they lined back up the way they came out.

airdave · Jan 8, 2016

airdave said:
Just got it all back together and it seems to be working fine. 1st time in a long time that I've seen the selector switch go through all the lights, diagnostic when starting, before staying on where I put it - 2wd! I called my local shop that specializes in GM only and asked him about the gear indexing inside the encoder assy. He asked if it was working ok before and I told him yes. He said to just put it back together and it should be fine as the encoder knows where it needs to be and it's not a problem if it's only off 1 1/2 teeth.

Just a little fyi for you guys wanting to do this repair. It's really not that hard but it did take me about 2 hrs. I'm 62 and don't get up off the floor real well anymore. Just be sure you have the proper tools before starting! I used a 15mm socket with a swivel 3" extension for all the bolts. You'll also need a T15 torx bit, and 11mm socket for the u-joint bolts.

Use the above illustration and instructions - EXCELLENT PICTURES AND WRITE UP!

Dave

UPDATE JAN. 8, 2016
I just returned from a 10 day trip up into Oregon where I had to use my 4wd hi often, as well as the Auto 4wd. It worked perfectly! So, that being said, apparently it's not critical where your large gear lines up to the timing mark on the case - however, make sure you have put the transmission and transfer case in neutral before starting this easy replacement! I would say, if you are skilled enough to be able to change out a driveline, or install a water pump, you should be able to do this job.

Snn5 · Dec 4, 2016

Just replaced my encoder today. This write up was perfect, however, I installed with the connector on the inside...backwards/reversed. I never saw the TOP label on the harness till AFTER the 3rd time I took it off to find out why it was grinding. Works now, for now. Seems someone had already replaced it before given the black ink marks on the gears. I looked at the old ring...had some chipping/fading around the tracks and the brushes looked a little mucked-up. Buttons are new and ring is new, so if this happens again soon, the TCCM is the go-to I'd think.

Snn5 · Dec 6, 2016

Wanted to add these 2 inside photos. You can see some permanent indentation from the brushes and what looks like eaten/corroded-away circuit track. I didn't have long tracks like the OP's, just the stationary scoring. I also found a fair amount of black smut, like you'd find in the dimmer knob on the headlight switch on its circuit board. There is a bit of muck or plastic stuck to the brushes as well it seems. I don't know if this is from non-use of the 4x4 system or what.

Soules75 · Jan 3, 2017

I just replaced the encoder motor sensor in my 2004 Silverado. I even did so without removing the driveshaft, which was nice. Anyways, for the last couple of days everything has worked flawlessly, that is until this morning when I got the Service 4WD message. So now I am hoping you guys can maybe help me troubleshoot further. But let me give some quick backstory first.

Here's the thing, when this problem first started a couple years ago, it would only happen on occasion. I'd restart the truck and it would work again, and when it worked, it worked flawlessly. That led me to believe the issue was probably electrical and not mechanical. Over time it became more frequent, and eventually got to the point where the switch would light up when the truck started but then immediately the lights would go out and the switch was unresponsive along with the Service 4WD message. This would happen the second I started the truck, and did so consistently (every single time) for like a year. I've already tried resoldering the switch, and that didn't do anything. The encoder motor sensor definitely seemed to semi-fix the issue, as I've only seen the Service 4WD message once in the last few days since replacing it, and prior to that it wouldn't work at all. But apparently it isn't 100% solved...so what now?

1. Do I need to have it reprogrammed?
2. If the new encoder motor sensor seemed to solve the problem temporarily, does that help somehow narrow down the problem? It obviously helped...but why didn't it solve it completely? Perhaps fiddling with everything down there moved around some wires, maybe a wiring problem?
4. Do I maybe have a problem with the TCCM?

Any insight or ideas would be so appreciated. I am so annoyed! I just want my truck to be a truck again!

Snn5 · Jan 3, 2017

If you have never replaced the push button switch now is probably the time to do it as resistance in each button is different and may have altered over time causing the issues you have now. If the lights don't come on at all on the switch then maybe the transfer case control module is at fault but I would start first with the switch as usually that or the encoder sensor is the issue. You can find a new Switch on eBay for around $25.

Soules75 · Jan 3, 2017

But doesn't it seem like a huge coincidence that after a year of consistently not working it suddenly started working right after I replaced the encoder motor sensor? I mean if the switch is the culprit, why would replacing the encoder motor sensor suddenly make it work? Granted it threw the Service 4WD message again a couple days later, but still. And while it has been working these last couple of days, the switch has worked perfectly.

I totally appreciate the help, just playing devil's advocate here. Thoughts?

Snn5 · Jan 3, 2017

Mine had done the exact same thing being intermittent and sporadic. Replacing the encoder sensor finally fixed the issue after I had already replaced the 4 wheel drive switch. It's entirely possible you had two bad parts one worse than the other but like I said I was in the exact same situation replacement parts is what rectify the issue.

Soules75 · Jan 4, 2017

I decided to crawl under the truck today and check out the ground wires that I've read about people having issues with. I live in Wisconsin so mine were quite rusty and dirty. The metal frame they attach to was particularly dirty and covered in rust. I removed the bolts and sanded the bolts, washers, wires, and the frame where they attach with my palm sander to remove the rust and cleaned then up. I put it all back together and am hoping that clears up the issues.

I drove to my dads to drop something off and no service 4wd, but then again he lives one road down from me.

I am not going to hold my breath and expectations are low, but I figured it was worth a shot...and free and easy. I'll report back after my commute tomorrow. That's the real test.

Snn5 · Jan 4, 2017

I also cleaned the same two bolts and put Dielectric grease on them and then coated them with clear spray that didn't seem to do anything for me in the beginning as that was the first thing I did. I had replaced the switch before but the issue persisted so I changed the encoder sensor and changed the switches because the back lights and mine had burned out.

Soules75 · Jan 4, 2017

Yea mine were really rusty and dirty so who knows, maybe that was my issue? I will say that it does sound a bit different when I switch between 2 and 4wd than it did before I cleaned everything. I can definitely hear things engaging under the truck. It is louder and stronger sounding. Maybe a good sign?

Soules75 · Jan 4, 2017

Unfortunately, I got the Service 4WD this morning again. UGH! I hate this issue. I noticed that since replacing the encoder motor sensor, the Service 4WD light has come on three times and every time it was about 20-25 minutes into my drive. Not sure if that means anything? So here's what I have tried to date, in order:

- Took apart and re-soldered 4WD switch (no change)
- Replaced encoder motor sensor (got it working again, but now it stops working after about 20 minutes of driving)
- Cleaned rust and dirt off of ground wires, bolts, washers, and frame where they attach (no change)

Before the Service 4WD message comes up about 20 minutes into my drive everything works perfectly, so I feel like the encodor motor, transfer case, etc. are probably fine. At this point I'm thinking the switch might be the cheapest/easiest next step. Then if all else fails...maybe TCCM?

Should I gamble on replacing the switch next or just pony up the $100 to have a dealership pull a code for me? Anyone with more knowledge than myself know why the encoder motor sensor replacement seems to have delayed the Service 4WD message by about 20 minutes?

bmerr98 · Jan 4, 2017

Much as it pains to say it, you might be money ahead spending the $100 for professional diagnosis. I agree it's probably electrical.

Snn5 · Jan 5, 2017

I'd get a new $25 switch from eBay. The resoldering might not have gone as well as hoped.

HOW TO CHANGE ENCODER MOTOR/SENSOR

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