Another Crank No Start | OBD2 No Comm + Xmas Tree Inst Panel w/Bonus ‘It hasn’t run in months’

Ok this seems to confirm we either have a short on the 5v ref circuit or a failed PCM.

Next step is to start unplugging 5v sensors while monitoring the 5v ref circuit, we can start with the Secondary Air Injection switching valves on the right side of the engine.

 

To confirm, this would be the same setup as the 5v testing I was just doing - black to batt ground and red to.....whichever 5v is easiest for me to get to?

I had to look up left and right side of engine View it as if I'm sitting inside the truck.

Too funny - I was actually just poking around on this Secondary Air Injection thing saying to myself "I wonder wth this thing is"

 

Correct, I would also expect if you clear the short the CEL should come back on but this may take a key cycle.

Yes, left is driver's side and right is passenger's side.
Picture of the valves for reference.

 

Same result with 1.23 roughly. Both unplugged.

 

Ok, throttle body, cam sensors, and accelerator pedal position sensor are also on the 5v circuit.

 

I located the throttle body on the back of the engine, but I can't quite reach it from my cinderblock. Even though no part of me wants to, I'll pause here and continue in the morning with a proper stepladder before I break an ankle.

I will report back tomorrow....or later today.

Thank you so much for this

 

Throttle body is on the front of the engine, you have to remove the appearance cover to see it.



The cam sensors are under the throttle body, you have to remove the air filter housing to access them.


To remove the air filter housing loosen the 2 clamps circled in yellow, the 2 bolts circled in red, 2 hoses circled in blue, and unplug the connector and clip circled in orange.

 

Thank you for the detailed info. I didn’t realize I was looking at a 1998 tacoma for my source. I’ve been unplugging the sensor and then turning the key to test this. Is that correct or should the key already be on and I unplug it then? So far the throttle position is the same when unplugged. And same for accelerator.

 

That's fine, you should get your 5v back if you unplug a shorted sensor.

 

Both cam sensors test at that same “starting at about 1.15 and jumping to 1.20 then crawling to 1.23”

Fwiw-the plastic tubing around the TPS is all dry rotted and you can see some of the wire through the tape underneath. I didn’t see any damage to wires but I guess that would have been prevalent when it was unplugged and tested.

I’m hoping there are overpriced specialty tools available for removing some of these wire harness clips.

 

I'm assuming you mean the wire loom, that's pretty common for that stuff to go to pieces when it gets some age on it due to the heat in the engine bay.

Assuming you mean the clips that hold harnesses in place? Not really, a right angle pick or small flat screwdriver are usually the most effective on the Toyota ones.

The only other 5v sensor that's left is the Canister Pressure Sensor on the Leak Detection Pump, that's no fun to get to but we can unplug IH1 behind the glovebox to eliminate it.

 

Unplugged the canister sensor thing. Same thing

 

Dang, really looking like the PCM is dead at this point.
We will need to check the 5v wires for shorts to ground but first since we know the CAN system is shorted lets check the resistance of pins 6 & 14 of the DLC with the PCM unplugged, that will tell us if the PCM is shorting it out.

 

I unplug all of the harnesses from the pcm?

 

Well the CAN lines are on E14 so you could just unplug that one to isolate the PCM from the CAN bus.

 

Forgot to ask does the battery stay connected or do I disconnect it?

 

It would be best to disconnect it when checking CAN resistance to avoid erroneous readings.

 

I know continuity doesn’t involve a ground per se in this instance, but if I wanted to retest one of these 5v connections, could I use one of the ground pins we tested before on the ecm instead of connecting to the battery? Since they tested good?

 

Yes.
What were the results on the CAN with the PCM unplugged?

 

It looks like 40? Batt unplugged. E14 disconnected. Pins 6 and 14 with meter on ohm setting