Inhbitor Relay in the Starter Solenoid Circuit
1992 Nissan Sentra XE,  GA16DE, Engine Code "E" 


One morning the engine would not start. There was no "click" from the starter solenoid.
All electrical devices: lights, radio, etc. worked normally.  There were no blown fuses, 
and the battery tested fully charged.  So the starter solenoid must be bad, I thought.

I turned to my Haynes manual to study the starter. The text mentioned the manual
inhibitor switch that disables the starter solenoid except when the shifter is in park or neutral.  A quick check of the inhibitor switch indicated that it was working. 

I went to my Nissan subscription at All Data.com and there I discovered that this car
has an Inhibitor Relay. This electric inhibitor relay works in the same circuit as the
manual inhibitor switch.  So either the switch or the relay can prevent the starter
solenoid from working.

Next I checked the wiring diagram in the back of the Haynes manual and sure enough
there is a solenoid circuit containing an inhibitor relay - although it wasn't mentioned
in the starter circuit text.  

Next, I began searching the engine compartment for the inhibitor relay.
Eventually, I found it. 

The inhibitor relay is the last relay in the relay box, to the right of the white line that I added to the picture.
The relay box was easy to open. It has plastic snaps at each end of the box cover.
The inhibitor relay is gray. It
is held in place with a plastic snap. Use a small screwdriver to force the snap away from the housing, while pulling the relay upward.

I was fortunate. See the small Phillips head screw in the bottom of the relay?

That screw had backed out and it
was laying in the bottom of the relay box.

I replaced the screw, plugged the relay into its socket, and the starter has worked every day since.

I don't know what that screw is for.
I've worked with relays in electronics for many years and I never had one that used that bottom screw.

It is possible that the screw had nothing to do with the relay working. It's possible that simply removing and replacing the relay caused the relay to make connection that had failed over time. Anyhow, the screw is in, the relay is in, and the starter works.

There are tests that can be done to find if a relay is working.  You need to follow a diagram
and use an ohmmeter and a voltage source to do the testing.  That goes beyond this single
Web page.
Posted October 14, 2008

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There are two diagrams below. The first one is for a 1992 Sentra that uses the
Inhibitor Relay and the Inhibitor Switch. (This one from my GA16DE engine.)

The second diagram is for a 1992 Nissan that uses the Inhibitor Switch without
the Inhibitor Relay. (I don't know which models use the second diagram.)

(ABOVE) If for any reason the Mechanical Switch is not closed, the 12 volt Relay will not have a path to ground and the Inhibitor Relay will not allow current to flow to the starter solenoid. When adjusted correctly, the Mechanical Switch Contacts are closed in only Park and Neutral. 

So both the switch and the relay must be closed for the starter solenoid to operate.

(BELOW) In this circuit, there is no 12 volt Relay. You have a Mechanical Switch only, which is closed in Park and Neutral to furnish current to the starter solenoid.  

I don't know which Nissan models use this configuration.

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