pre-heater out of control (1 Viewer)

[jblueridge]

On Sunday I noticed my dash volt meter was reading low right after I started the truck.
It showed low for 3 or 4 minutes, then jumped up to normal.
It was the pre-heater system drawing power, but the Pre-Heater light does not come on.

Yesterday I checked the water temp sensor and it showed a sensible 3K ohms.
That is within spec.
I disconnected the wires that feed the pre-heater's toaster wires.
When I started the truck the volt meter showed normal, and the pre-heater light came on and stayed on.
Reading the manual, the light staying on informs the driver there is a problem with the system... so that is working properly.
With the FSM I will continue to do tests when I get time.

I am wondering if anyone has run across this before.

 

[svsisu]

I had a dead a short in the glow plug relay (LH side, upper fender well on LHD truck) that pulled my batteries down flat. It was pretty tricky to find where the issue was. My truck originally had a 3B but a 1Hz had been swapped in. The PO never had the glow system working correctly and the relay was not connected when I first got it. I had connected the relay and the glow system seemed to be working for about 2 weeks, then the short happened. I guess that's why it was not connected in the first place. I also had a minor voltage drop happening through the not working digital clock. Unplugged both and all good, except I have no glow plugs working at this time. I'm planning to install a wilson switch before winter comes along.

Maybe check for a short in the relay or glow timer.

 

[jblueridge]

That is some good info.
The truck had been sitting for about 1 week and the batteries had to be charged just to get it to start.
After that, I saw the major current draw.
Also, for the past few months, my digital clock sometimes shows up as maybe half as bright as it should be.

I'll check the relays using FSM as a guide.

Thanks!

 

[svsisu]

That is some good info.
The truck had been sitting for about 1 week and the batteries had to be charged just to get it to start.
After that, I saw the major current draw.
Also, for the past few months, my digital clock sometimes shows up as maybe half as bright as it should be.

I'll check the relays using FSM as a guide.

Thanks!

My batteries were dead flat after sitting over night. No click, nothing, and it had been fine the previous evening. That is kind of what I saw with the major current draw- I would charge the batteries, then check voltage with the charger removed and could watch the voltage drop rapidly. It was crazy and kind of scary. I was happy when I found the culprit. Hopefully this gets you pointed in the right direction, good luck.

 

[jblueridge]

During lunch time, I used an ammeter and measured only 22mA coming from the batteries with no key and everything turned off.
This is the same current draw I measured 6 months ago after installing 12V radio.
It's the Toyota clock and the 12V radio "memory" using power.

Checking relays is next.

 

[jblueridge]

I got at the relays and did the checks as shown in the FSM.
They check out as okay; no shorts.

I took the glove box apart and swapped the Pre-heater Timer out for a used one that was working when removed.
Started the motor and saw the same behavior: dash Voltmeter stays down at the very bottom of the "normal range" for a long time then pops back up to about 28 volts. The dash Pre-heater light does not come on.

I think next I will run a jumper to essentially short circuit the water temp sensor.
That should have the effect of making the Pre-heater Timer think the engine is already warmed up.

 

[jblueridge]

So I bypasses the coolant temp sensor with a jumper wire.
With almost no resistance from the sensor, the pre-heater timer box believes the engine is warm and does not engage the pre-heater relays.

So the problem remains that the pre-heater heating elements come on when the engine is started but the dash light does not light up.