Gear Selector Indicator Not Showing Up With New NSBU Switch

[Animals1234]

Hello guys,

I have an 05 Duramax and the last couple of weeks I've been having a strange issue with the gear selector light. When I start my truck up it'll show all the gears but it won't show which gear I'm in until a few minutes later. Once those few minutes have gone by it'll underline which gear I'm in. So based on previous reading I've done here people were saying that the NSBU could be possibly worn out or defective. I purchased a new switch from Dartco and swapped it out. However I'm still having the same issue as I was before, waiting several minutes until the gauge indicates what gear I am in.

If I force the truck into gear without the gauge indicating the gear I'm in it'll say "service brake system" then it'll go away, followed by showing what gear I'm in. The truck will shift through all the gears and isn't limping either.

Would there be any other recommendations on what to check for? I've check my entire brake system, fluids, and anything wiring related to the brake system to make sure it wasn't from the message my dash was telling me. Transmission was rebuilt in 2016 and this is the first issue I've ever had with it. I have a GM Tech 2 on hand if there's any special functions I can try out.

 

[Chevy1925]

i would see if the tcm or cluster is getting a good signal. sounds like the display is not working correctly but the service brake system throws a curve there. you can use the tech 2 to make sure the tcm is receiving a signal on what gear its in when you move the gear selector.

 

[Animals1234]

Update:

So here are some things I've tried since the initial attempt.

I looked at the pins going in the wiring harness going towards the TCM. From what I initially saw there was some residual oil in the pins. So from there on I cleaned the plastic piece that holds the pins in place and reconnected them. Even though it was cleaned out it's still doing the same thing. I checked with my Tech 2 once the gear selector indicator was labeling what gear I was in and it was receiving signal. From park to first gear my tech 2 was receiving a signal.

My next plan of action is to replace the ignition switch and inspect the shifter area if there's any chafed wiring that would cause this.

 

[Animals1234]

Here's the next thing I check from some other posts I saw on the forum

Checked the ignition fuse on the left part of the dash. It looked good there.

 

[Animals1234]

Here is a photo for reference for what it's doing, before and after

 

[Ron Nielson]

I don't have one, but the Tech2 should show somewhere the gear that has been selected, and perhaps separately which gear is engaged. Does Tech2 allow you to select specific computers to communicate with? Select transmission and see if you can communicate with the transmission and see what info is available.

Where exactly is this connector with oil in it? Brake clean or similar should clean out any oil. You shouldn't have oil in the connectors.

 

[TheBac]

Could it be a sign of an intermittant ground connection? The "Service Brake" warning makes me think that.

 

[WolfLMM]

Go ahead and inspect the shifter for excess wear and a stretched shift cable too. Had the same problem on my 2001 truck (minus the service brake message) couldn’t get nsbu properly adjusted till I installed a new shift cable. D was N and I would have to pull down to 3 for the truck to be in D. Pulled my hair out for a couple weeks on that one. I have a thread on here about it I believe. It’s 5-6years old though. Just something to check while you are in there. The brake system error seems to point elsewhere though.

 

[dndj]

I checked with my Tech 2 once the gear selector indicator was labeling what gear I was in and it was receiving signal. From park to first gear my tech 2 was receiving a signal.

What does the Tech2 read for gear indication when the gear indicator in the cluster is not present?

 

[Animals1234]

I don't have one, but the Tech2 should show somewhere the gear that has been selected, and perhaps separately which gear is engaged. Does Tech2 allow you to select specific computers to communicate with? Select transmission and see if you can communicate with the transmission and see what info is available.

Where exactly is this connector with oil in it? Brake clean or similar should clean out any oil. You shouldn't have oil in the connectors.

Once the gear selector is underlined it shows which proper gear it's in on the tech 2. If the gear selector isn't underlined then it just shows park.

Could it be a sign of an intermittant ground connection? The "Service Brake" warning makes me think that.

That's what I'm starting to lean towards. I was told to check all the grounds on the truck to see how they were. I haven't had the chance to do that yet either.

Go ahead and inspect the shifter for excess wear and a stretched shift cable too. Had the same problem on my 2001 truck (minus the service brake message) couldn’t get nsbu properly adjusted till I installed a new shift cable. D was N and I would have to pull down to 3 for the truck to be in D. Pulled my hair out for a couple weeks on that one. I have a thread on here about it I believe. It’s 5-6years old though. Just something to check while you are in there. The brake system error seems to point elsewhere though.

I need to do this. A while back I had messed up the clockspring and haven't gotten around to changing that either. Hopefully this weekend I have time to do the clockspring and inspect the shift cable for any wear. Could be a good time to install a tapshifter too.

What does the Tech2 read for gear indication when the gear indicator in the cluster is not present?

Park in all gears when cluster is not present.

I'll keep you guys posted to see what happens. Work picked up and haven't had as much time to mess with the issue

 

[Animals1234]

Update: new TCM fixed the issue. So the thing's I've replaced on my truck are:

NSBU switch
Clockspring (had an airbag light I finally got around to)
Ignition switch
TCM


Do you guys often see 01-05 TCM's go bad? Usually I see 06+ go bad. Weird how it was throwing random codes but now the truck is all good with no abs and service brake system messages.

 

[dndj]

Thanks for reporting back. Guessing that the ABS codes could have been a result of the broken TCM's inability to pass the vehicle speed sensor data onto the the ECM and ABS modules which use that as input.

I don't have any insights as to the general reliability of TCMs of LB7/LLYs.

 

[tduncklee]

Hello guys,

I have an 05 Duramax and the last couple of weeks I've been having a strange issue with the gear selector light. When I start my truck up it'll show all the gears but it won't show which gear I'm in until a few minutes later. Once those few minutes have gone by it'll underline which gear I'm in. So based on previous reading I've done here people were saying that the NSBU could be possibly worn out or defective. I purchased a new switch from Dartco and swapped it out. However I'm still having the same issue as I was before, waiting several minutes until the gauge indicates what gear I am in.

If I force the truck into gear without the gauge indicating the gear I'm in it'll say "service brake system" then it'll go away, followed by showing what gear I'm in. The truck will shift through all the gears and isn't limping either.

Would there be any other recommendations on what to check for? I've check my entire brake system, fluids, and anything wiring related to the brake system to make sure it wasn't from the message my dash was telling me. Transmission was rebuilt in 2016 and this is the first issue I've ever had with it. I have a GM Tech 2 on hand if there's any special functions I can try out.

I have an 07 classic with the exact same symptoms. I discovered the wiring harness had some bare wires and were shorting out above the transmission. Try moving the wires and see if anything changes.

 

[Animals1234]

I did, it was a new TCM that fixed my issue