Glow plug relay does not engage unless keys are switched on and off various times from off to run position

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Jul 22, 2020
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hi bitogers,

I have a 1990 corolla diesel.

Is it that sometimes when the engine is cold, the glow plug relay does not turn on, the first time the key is switched on from the off to run position, the glow plug relay should turn on and the glow plug light on dashboard should light on, what happens is that I have to turn the key sometimes about 30 times for the glow plug light on dashboard and glow plug relay to turn on. I dont know if it could be the key tumbler, some wiring, the glow plug controller module, glow plug relay or what?
Also the diesel water filter dummy light on dashboard doesnt turn on as it should when key is switched from off to run position and turns on with the glow plug dashoard dummy light after cycling the key 20 times from off to run position in key tumbler.

What would cause the problem?

Thanks

Jorge
 
gp relay.jpg
 
Take the controller module apart and replace any electrolytic capacitors and resolder ALL the connections on the circuit board.

Though we didn't have diesel Corollas in the USA, problems with the circuit board were a very common issue on the Toyota A/C compressor control modules of the day.
 
I am leaning more towards the ignition switch as the diesel water filter dummy light on dashboard also doesnt come on unless the key is cycled from the off to the run position various times.
 
Take the controller module apart and replace any electrolytic capacitors and resolder ALL the connections on the circuit board.

Though we didn't have diesel Corollas in the USA, problems with the circuit board were a very common issue on the Toyota A/C compressor control modules of the day.
Maybe this glow plug controller could be an issue.

The temp sensor was damaged so it was replaced but the problem finda itself still there.

On a different topic, could a bad a/c compressor control module make an a/c not cool enough? Maybe i could check this a/c control module.

The only other possible causes are the ignition switch and the glow plug controller.

The temp sensor was disconnected and the glow plugs automatically always regardless of temperature, though a correctly working system uses the temp sensor input to decide when to glow.

When engine is cold all the dashboard lights won't turn on, only when the engine gets to operating temperature, strangely all the dashboard lights come on.
 
Thanks, relay works fine.

Take the controller module apart and replace any electrolytic capacitors and resolder ALL the connections on the circuit board.

Though we didn't have diesel Corollas in the USA, problems with the circuit board were a very common issue on the Toyota A/C compressor control modules of the day.
The vehicle does not have a separate preheating timer for some reson, as other diesel corollas. apparently this one has the glow plug timer integrated into a box that says emissions control:
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The car electric technician opened it up and could not see any bad solder points or burnt capacitors. I took it to a televisio electronic tecnician and asked him check for bad capacitors.
 
Pics of the inside of the apparent glow plug controller
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The computer checked out and the auto electrical tecnician stimulated the computer and it did send a signal to the glow plugs, so the glow plug timer works aparrently.

The auto electric techinican said that maybe an electrical short or bad conection could cause this problem.

Since this car, did have RHD steering before it was converted to LHD, during the conversion perhaps the electrical system got modified in some way that may have caused this.
 
At least on MB diesels, the GP relay is a pretty robust part. I can’t imagine why it wouldn’t on a Toyota.

I assume the relay has some sort of afterglow feature that sets the on time and if they remain on after start. If so there is probably a temperature sensor in the mix here that should be evaluated. Those 30 tries could be some combination of solenoids and other things moving just enough to get a good read on a temperature sensor or other connection. I know that the duration that these sorts of dummy lights stay on for will vary, and I’ve seen it on my Cummins trucks as well.

Have all GPs actually been evaluated through the harness? On MB relays, the system compares the resistance of all the plugs to #1. If there is a mismatch then the light doesn’t come on in a consistent manner.
 
On a toyota it looks pretty robust too. When the system worked fine, the afterglow feature worked. Now that i have to jump the gp relay, the afterglow function does not work.

The temp sensor got changed for a brand new oem one.

Havent checked each inividual gp., recently, though they checked out fine simetime ago, and when the gp relay gets jumped, the engine fires up instantly.
 
Put a test lite in line with the relay coil. Is it receiving command to engage? And does the coil see both + and -?
 
The circuit board and components look fine-no burn marks or burnt components. You say you replaced the temperature sensor with an OEM unit. What was wrong with the original temperature sensor? Can you find another care like yours's and swap temperature sensors?
 
The circuit board and components look fine-no burn marks or burnt components. You say you replaced the temperature sensor with an OEM unit. What was wrong with the original temperature sensor? Can you find another care like yours's and swap temperature sensors?
The old temperature sensor had a little crack on it. Difficult to find another car like that. The auto electric guy told me find a electrical wiring diagram to see how the glow plug controller gets connected. I ordered some original toyota electrical wiring diagrams and hope that i can find the diagram for this application.
 
I just noticed at night time when no key find itself inserted in the car and i pump the brakes that the tachometer lights and the cigarrette lights turn on.
 
That's either a bad ground (at the taillights) or use of the wrong bulbs or other shenanigans has crossed the circuits.
 
Hmmm, there seems to be an unsoldered connection in the center of the last large picture.
 
So i Just got the car back from the shop and they replaced the alternator which found itself bad as it gave 16 volts; and apparently a shorted out coolant sensor line helped to cause the glow plug timer to not function.
 
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