Z31/TCU php

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Z31 Repairing the Timer Control Unit(TCU)

The Z31 uses a time control unit for many small functions throughout the car. As these cars age, the electronics start to fail. Here we will discuss on of these failures.

Timer Control Unit Control

• Intermittent Wiper Control Timer
• Interior Lamp Timer
• Door Key Hole Illumination Timer
• Illumination Control Timer
• Light Warning Timer
• Key Warning Timer
• Seatbelt Warning Timer
• Rear Defogger Timer

Pro Tip: Finding the Timer Control Unit (TCU)

The Factory Service Manual (FSM) makes it sound simple:

• Remove R.H. dash side cover and remove blower motor.
• Remove time control unit with harness connected.

Sounds easy, right? But if you can't spot the TCU after these steps, you’re not alone! Here’s how you actually get it out:

• Remove the glove box.
• Remove the lower passenger trim panel.

- Disconnect the wiring harness on the right side (the one with the 4 large plugs in it). Unscrew it from the firewall.

- You can now see the bottom corner of the TCU (just barely) if you lift up the rubber pad:

- Here comes the fun part. You have to remove the ENTIRE fan assembly to get to the TCU. This means not only removing the motor, but EVERYTHING above it. There are two screws holding it on attached to the firewall (where the passenger’s feet would be) and a third above the glove box. (Below: bad photo, but you’ll see the screw looking straight up from where the glove box was.)

• Disconnect any electrical connector that gets in the way. You may also want to disconnect the vacuum line (for auto AC).
• Lift up on the blower unit and push back about 1/2". This unhooks it from the top.

- Wiggle and curse it down until your passenger floorboard looks like this. You don't have to completely remove it from the car, but get it low enough to get to the TCU.

- NOW, you can get to the TCU to remove it. There is only one screw holding it on, and the wiring harness.

- Now that it’s out, curse the engineers a bit. Here is a picture of the TCU:

• Put in your new (or old) one and reverse the steps. Might want to check and make sure the replacement works first. And, pro tip: disconnect the Autometer gauges or radio you hooked up that caused it to blow in the first place, or you’ll be doing this again!

Tech Tip: Repairing Your TCU

If you’re handy with electronics, here’s what’s usually wrong inside the Timer Control Unit (TCU):

• Open the case and inspect the transistors.

-

• The transistor riveted to the aluminum heatsink is almost always the culprit—it’s likely cracked or visibly damaged.
• Unsolder this transistor. On mine, the part number was

NEC C2654. - Replace it with any NPN TO220 transistor rated at 8A or more (the NEC was rated for 15A, so aim high for reliability). Hfe should be above 10. A 10A NPN Darlington has worked for others too. -

Pro tip: Always double-check your replacement’s specs, and test the board before buttoning it back up. Congrats—you just saved a rare part from the scrap heap!

Sources Used

1984-1988 Nissan 300ZX Factory Service Manual

• Writen by: Matt Brown