Thought I might find some insight here. 2002 Blazer LS 4WD. Transmission was replaced maybe 3 years ago.

Indicator lights on dash for Park and Neutral do not illuminate. R, D, 1, 2 and 3 light up normally.

Vehicle starts in park or neutral, not in other gears, as it should. Reverse lamps work. Computer, however does not know if trans is in park or neutral. I had friend check this with Snap-On scan tool. Unfortunately, we could not go into depth with scan tool as his boss showed up...

When I checked under the vehicle, the lower (4 wire) connector on the neutral safety switch was disconnected. My first reaction was "Yay! Here's an easy fix." but reconnecting the wire made no difference. I wonder if the trans installer (dealer) left it off on purpose...

I've read about instrument cluster problems here, but wouldn't that affect all indicators (not just [P] and [N])? ... and where does the computer get the signal from?

Many thanks in advance!

 

Gear position data is sent from the transmission to the PCM, (Powertrain Control Module). The data is shared with the BCM, (Body Control Module) and sent to the instrument cluster circuit board through classII communications. More than likely the problem is in the indicator logic module inside the cluster.... poor solder joint, bad logic module, etc. There are companies online that refurbish instrument clusters... send them yours and they send you a refurbished one. Other options include new clusters from Dorman, GM dealers, or used from a boneyard.

 

Awesome! Thanks so much for taking the time...

I'm a pretty good electronics tech, and the instrument cluster doesn't look too hard to remove, so I think I'll try checking for cold/broken solder joints first. Make sense?

Watched a couple of YouTube videos about removing the cluster. Any "gotchas" I should know about?

 

R&I of the dash trim & cluster is pretty straight forward: The bezel is attached with a bunch of 7mm screws, and some snap clips that just pull out. Once the cluster is out, there's a black plastic piece that covers & protects the entire circuit board. It's attached with tabs that must be released to remove it. The printed circuit board is attached to the cluster with the same type of clips, and maybe a couple of small screws. Once the board is removed from the cluster, everything is completely accessible. The indicator logic module has maybe 20 solder joints covered with a clear silicone rubber material to seal out moisture. Probably be a good idea to replace all of the #194 illumination bulbs while it's all apart Take your time and you'll do OK. Good luck and post your results.

 

Thanks again! Great tip about the bulbs too. Will buy them in advance.

Working all weekend, hopefully will get to it on Monday and will definitely post results.

 

There are either 6 or 7 bulbs, can't remember for sure

 

Just to follow up on this... took the cluster out a couple of nights ago. Super easy to get it out. Found three of the 4 screws that hold it in were laying on the bottom part of the dash, under the steering column.

Went over the whole thing wearing strong eyeglasses, but couldn't find any bad solder joints (I know what cold/broken solder joints look like too). Re-soldered a bunch just for the heck of it...

I bought a bunch of 194 bulbs, but found that the bulbs inside were PC194 which are permanently attached to the sockets. None were burned out, so I just put them back in. It's easy enough to change them anyway.

Bottom line: Shift indicator behaves exactly the same... I didn't fix anything, didn't break anything, and learned how to R&R the instrument cluster. My gut is to go ahead and try the neutral safety switch next (before sending out the cluster). What do y'all think?

If I knew how the NSS worked, I could jump wires to diagnose it. Anyone have a clue or a diagram?

Thanks!

 

If the starter only cranks the engine in park & neutral, the reverse lights work when you select reverse, and the transmission shifts properly, the switch is working. You can also check with a capable scan tool to see if the VCM recognizes gear shift position.

Forgot about the PC194 bulbs, sorry. I service a fleet of Astro and Safari vans and 2002 uses plain old #194 bulbs for instrument illumination.

 

Franco
Did you find anything? my blazer is doing the same thing but more. Mine has no park or neutral light but I also can not shift my transfer case in to low range or neutral and after you shut the truck off and you look real hard the odometer lights up but very faint

Thank's Pete

 

Hi Pete,

Sorry, have not done any further diagnosis. I've been busy and it went on the back burner... Truck runs and shifts normally. Can go into and out of 4WD Hi (good thing in the recent snowstorms...). Still have no indicator lights for P and N and lately, if I shift down to 1, the indicator light stays on 1 even when shifting up to 2 or 3. The transmission shifts, but the indicator sticks.

If I shift up to 3 from 1, the 3 will eventually illuminate, but it doesn't change right away. D lights up normally, as does R. Haven't tried 4WD low lately... It was working back when I first posted, but that was a few months ago. Will try it tomorrow. The transfer case control module needs to know that the transmission is in neutral before shifting into 4WD low.