How to diagnose no start & bad clutch bypass system (56K warn)

[g6civcx]

Please proceed at your own risk. Zilvia.net and author not responsible for content or misuse.
-------------------------------------------------------------
Application: model year 1989 to 1994 Nissan 240SX S13 cars with manual gearbox originally sold in the USA

Symptom: no start with key. No starter click. Engine does not turn.

Cause: possible faulty clutch bypass circuitry.
-------------------------------------------------------------
Background

The purpose of the clutch bypass system is to prevent the vehicle from being started without depressing the clutch pedal. The system prevents power from going to the starter unless the clutch pedal is depressed.

A no-start problem is usually caused by a faulty clutch interlock switch or relay.

http://www.nguyenconsult.com/zilvia//ClutchBypass/ClutchBypass1.jpg
-------------------------------------------------------------
Clutch interlock switch

The switch is located behind the clutch pedal as outlined here.

http://www.nguyenconsult.com/zilvia//ClutchBypass/ClutchBypass2.jpg

I removed the switch to show you what it looks like. It's activated when the black switch is depressed when you fully depress the clutch pedal.

http://www.nguyenconsult.com/zilvia//ClutchBypass/ClutchBypass3.JPG

The switch is mounted on by a 14mm nut. To adjust the switch position, turn the locknut clockwise while facing the pedal to loosen the locknut. Turn the switch to adjust its position accordingly. Make sure the clutch pedal strikes the switch at the bottom of the clutch travel. Tighten by turning the locknut clockwise.

Also check to make sure that the harness is correctly plugged into the back of the switch.

The most often cause for a no-start is the clutch relay switch falling off the path of the clutch pedal because the pedal bracket is damaged.

http://www.nguyenconsult.com/zilvia//ClutchBypass/ClutchBypass4.JPG
--------------------------------------------------------------------
Clutch interlock relay

The relay is mounted near the battery. E25 as shown here.

http://www.nguyenconsult.com/zilvia//ClutchBypass/ClutchBypass5.jpg

This is what it looks like. It's mounted under the apron of the fender by two (2) 10mm bolts. I removed it show you what it looks like.

http://www.nguyenconsult.com/zilvia//ClutchBypass/ClutchBypass6.JPG

This is the infamous blue relay that is notoriously prone to failure. You can remove it and replace it with a known-good. You can also test the circuit by jumpering the Brown/White and Brown/Yellow wires. If the vehicle can be started this way, the relay is faulty. Replace with a known good.
----------------------------------------------------------------------
For those who would like to bypass the clutch interlock completely, this picture is self-explanatory. Just remember that the vehicle can now be started in any gear and regardless of clutch position. ALWAYS REMEMBER NOT TO START THE VEHICLE IN GEAR!!!

http://www.nguyenconsult.com/zilvia//ClutchBypass/ClutchBypass7.jpg

[dolphin]

good write up!

[blownmotor]

Canadian s13's do not have that relay/switch combo I bypassed mines just to simplify things

[Lith]

Canadian s13's do not have that relay/switch combo I bypassed mines just to simplify things

Canadian S14 Zenkis don't have the clutch interlock either.. and I'm 90% sure the Canadian S14 Koukis don't have one either.

[yokotavia]

JDM silvias dont have it either.

good writeup tho

[nismoskyz]

no pics....

op update pics possibly, please?
thanks

[KeithDigital]

This is the infamous blue relay that is notoriously prone to failure.

Thanks! You helped me out a lot with your write-up. I had a bad clutch interlock relay.

Symptoms:
Car won't attempt to turn over. Had the battery tested and it was good, changed the starter and even checked and cleaned up the ground wires - still nothing. Sometimes randomly it would start, and most of time it would start with a jump-start. Ended up being the clutch interlock relay. I by passed it (just like the JDM and Canadian S13's are setup) and it starts every time now!

[g6civcx]

Good to know. The starter interlock relay will not let the starter crank at all. So you will have good battery check and the starter will pass the test if you pull it and take it to Autozone.

It could also be the interlock switch under the clutch pedal as well. Sometimes your clutch bracket gets fuxor and the switch gets misaligned.

[rocksteady_racer]

I also had a similiar problem with my clutch interlock relay. So I just ran it straight thru. But be careful if you're in the US not to say that to your inspection guy because it's technically illegal to have that safety feature disabled on your manual transmission. It's akin to not having an airbag in an airbag equipped car from the factory.

[jumboflan]

doesn't the OP mean Black/Yellow instead of Brown/Yellow.