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

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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.
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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.


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Clutch interlock switch

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



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.



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.


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Clutch interlock relay

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



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.



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.
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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!!!