TCU question - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

BoxMan · 08-18-2010, 01:19 AM

I've already searched all over this forum as well as others and I learned that if the Timing Control Unit or TCU (little white box behind the driver side kick panel) is fried, it will cause your dash light to malfunction. So I have a question regarding this TCU:
1) if this unit fails, will it not only shut off my dash light, but also my digital speedo?
2) How can I tell if my TCU is fried? Assuming I've taken it off and opened it up, what do I look for??

This is for an '89 coupe sohc.

please help, thanks.

BoxMan · 08-18-2010, 08:01 AM

Okay, check it out. I had a problem disconnecting the tcu from it's harness because it's hurting my fingers x(
Anyway, I happened to notice slight discoloration on the back of the module itself. The entire box is made of plastic and when this type of plastic is damaged or morphed (burned) you get discoloration like this.. I think. Could my theory be wrong? or is this box fried?

tommytwo40hands · 08-18-2010, 10:39 AM

Not sure on the speedo(it could just be that you have a bad HUD or your wiring is loose behind the cluster) but the TCU controls the dash lights, clilmate control, and the glove box light..You're gonna have to open it up and check for black discoloration somewhere on the board..they're a little bit of a pain to get open, the easiest way i found was to take a flat tip screw driver and pop each "latch" open one at a time..also make sure when you put it back together the board is lined up with the grooves inside the case.

BoxMan · 08-18-2010, 11:27 AM

Quote:

Originally Posted by tommytwo40hands

Not sure on the speedo(it could just be that you have a bad HUD or your wiring is loose behind the cluster) but the TCU controls the dash lights, clilmate control, and the glove box light..You're gonna have to open it up and check for black discoloration somewhere on the board..they're a little bit of a pain to get open, the easiest way i found was to take a flat tip screw driver and pop each "latch" open one at a time..also make sure when you put it back together the board is lined up with the grooves inside the case.

I think the speedo has a problem of its own. Anyway, I did what you suggested with the flat hit and that worked like a charm. However, I checked the board and it's as clean as a whistle.

I will inspect them once more to eliminate my TCU as the source of my problem. (Dashlight doesn't light up). So if it's not my TCU, what else could it be? Cluster Bulb perhaps?

Clutch Dog · 08-18-2010, 12:14 PM

Maybe.. dash dimmer? bad grounding. blown fuse

g6civcx · 08-18-2010, 12:33 PM

Quote:

Originally Posted by BoxMan

if this unit fails, will it not only shut off my dash light, but also my digital speedo?

Yes. No.

Quote:

Originally Posted by BoxMan

How can I tell if my TCU is fried? Assuming I've taken it off and opened it up, what do I look for??

The easiest way is to swap your TCU int a car that is working correctly. Don't put the good TCU into your car because whatever is wrong with your car may damage the good TCU.

240-J · 12-14-2012, 12:27 PM

Will the tcu cause your running light to go out as well and pop the fuse that runs them

08-18-2010, 01:19 AM	#1
BoxMan Leaky Injector Join Date: Oct 2008 Location: Rialto, CA Age: 31 Posts: 149 Trader Rating: (2) Feedback Score: 2 reviews	TCU question I've already searched all over this forum as well as others and I learned that if the Timing Control Unit or TCU (little white box behind the driver side kick panel) is fried, it will cause your dash light to malfunction. So I have a question regarding this TCU: 1) if this unit fails, will it not only shut off my dash light, but also my digital speedo? 2) How can I tell if my TCU is fried? Assuming I've taken it off and opened it up, what do I look for?? This is for an '89 coupe sohc. please help, thanks. __________________ Bone in and Bone out!

08-18-2010, 08:01 AM	#2
BoxMan Leaky Injector Join Date: Oct 2008 Location: Rialto, CA Age: 31 Posts: 149 Trader Rating: (2) Feedback Score: 2 reviews	Okay, check it out. I had a problem disconnecting the tcu from it's harness because it's hurting my fingers x( Anyway, I happened to notice slight discoloration on the back of the module itself. The entire box is made of plastic and when this type of plastic is damaged or morphed (burned) you get discoloration like this.. I think. Could my theory be wrong? or is this box fried? __________________ Bone in and Bone out!

08-18-2010, 12:14 PM	#5
Clutch Dog Zilvia Junkie Join Date: May 2010 Location: PNW Posts: 346 Trader Rating: (1) Feedback Score: 1 reviews	Maybe.. dash dimmer? bad grounding. blown fuse __________________ Mad Moody Science LLC In house is the best way.

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08-18-2010, 10:39 AM	#3
tommytwo40hands Leaky Injector Join Date: Jun 2010 Location: Springfield, MO Age: 32 Posts: 145 Trader Rating: (2) Feedback Score: 2 reviews	Not sure on the speedo(it could just be that you have a bad HUD or your wiring is loose behind the cluster) but the TCU controls the dash lights, clilmate control, and the glove box light..You're gonna have to open it up and check for black discoloration somewhere on the board..they're a little bit of a pain to get open, the easiest way i found was to take a flat tip screw driver and pop each "latch" open one at a time..also make sure when you put it back together the board is lined up with the grooves inside the case.

12-14-2012, 12:27 PM	#7
240-J Join Date: Oct 2012 Location: Los Angeles Age: 28 Posts: 6 Trader Rating: (0) Feedback Score: 0 reviews	Will the tcu cause your running light to go out as well and pop the fuse that runs them