'99 4x4 SR5 3.4L 5-spd

It starts great, with no codes present. But when it gets up to temperature it stalls and throws P0335 and P0340. I also got P1300 at least once, not sure if that happens every time.

After the stall it cranks but won't start.

After cooling down it will start right up again, but when it warms up the same stall and codes happen. Repeat.

I was suspecting timing belt, and reached out to a mechanic friend who said this is a common issue and the problem is actually the coolant temperature sensor (for the ECU), which would be relatively good news since I'm not ready to do TB on this one yet, except...I'm not seeing anybody talking about this diagnosis on the forums, so...

Before going further with the coolant temperature sensor, I am reaching out to see if that diagnosis holds water with the experts here.

I have the timing belt cover off, and the belt looks great. I have parts ordered to do the sensor:

89422-35010: Engine Coolant Temperature Sensor
90430-12005: Crush Washer for the Sensor
90430-12026: Crush Washers (4) for the fuel rail

video for the sensor swap:
How to Replace the Coolant Temperature Sensor on a Toyota 3.4L V6 - YouTube

Thanks in advance!
-Mike.

It's a possibility. Are you able to look at live data from the ECM? That would be the easiest way to verify if the engine coolant temp sensor is giving the ECM bad information.

Yeah, I can monitor temp and voltage in real time at the ODB2 port, so that's got to be live ECM data. What would I be looking for? I'm kinda thinking that, since I can see the temp going up that means the sensor is sending and the ECM is receiving, and therefore the sensor isn't the problem...?

I don't know if I can see freeze frame, and don't know what I'd be looking for if I can. That might be where I need to focus to figure it out.

That would be the temp the ECM sees. If you check it when it's been sitting overnight it should read close to ambient temperature and intake air temperature. I don't have a 1998 FSM but after looking at my 2000 FSM P0335 is "Crankshaft Position Sensor "A" Circuit Malfunction" and P0340 is "Camshaft Position Sensor Circuit Malfunction". You might start looking at wiring for those two.

Also, when you crank it after it stalls does the tachometer read anything?

Not to say your friend is wrong, but from the wiring diagrams I've used the engine coolant temperature sensor does not interact with the camshaft and crankshaft positions sensors. Even if the ECU saw a bogus temperature reading, like 400 degrees, it will not cut out the engine.

Do you have anyone nearby with same year and drivetrain model (2WD or 4WD) that you can swap out ECU's? It's a very rare issue but since these codes are so uncommon to have together at the same time like that, along with an igniter code, it could be internal damage to the ECU itself. You would need an ECU of the same year and driveline so a 1999 4WD ECU. Been wheeling through some tall water or flooding lately?

It's not the timing belt. Even if the belt jumps a few teeth it'll run terrible but it still runs. Won't normally throw a code other than misfires.

Interesting that you mention water, and I'm kicking myself for not thinking to bring it up, but...I did have water leaking from the top of the windshield on driver side during the tail end of tropical storms a couple weeks ago, before I caught it and brought into the garage. It was dripping over steering column, so could have potentially travelled to ECU or other wiring along the way.

By the way, the symptom has now changed.

I put the truck back together, including swapping in the battery from my '98, to do the tests that Mr Luck suggested (I confirmed that air intake and coolant temp were close to ambient when cold), but it cranked and wouldn't start. I just got a little pop and it threw the crankshaft position sensor circuit code. After that, I reset the ECU by disco/reconnecting the negative side and now it still just cranks, without throwing any codes.

So...troubleshooting. I don't suppose the ECU on my '98 would be any help? They are both 3.4L 4x4, but '98 is Auto (no lockers) and '99 is 5spd (with e-lockers).

Can ECU function be proven without swapping in another one? or...could the '99 ECU be proven good/bad by swapping into the '98?

My gut says I also need to rule out the crank sensor circuit.

Good times :-)

Both the wire pin location and the plugs themselves changed year over year. You could try, some years even have a 5th ECU plug while our 98's only have 4. The ECU is tucked laying flat right behind the glove box. You have to remove the upper glove box lid and disconnect some wiring but it's only like 5 10mm screws and some clips so not too crazy.

That's a bummer about the water leaks though. If it helps, the engine wiring is only on the passenger's side of the interior at the location mentioned above. If you do want to test the crank sensor circuit, you'll just need to unplug the corresponding plug from the ECU and use test leads from the plug in the engine bay (located just in front of the oil filter, yes it'll be dirty and messy) to the wire on the ECU. At least it's a simple circuit! Same goes from camshaft sensor.

Everytime I have an issue with shutting off hot and not starting until it cools off I look at the crank and or cam sensor and the igniter box.

That is classic crank sensor IMO.


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Thank you! Any tips on checking the crank sensor? That's going to be my Friday night.

BTW, I found a nice write up on the Igniter:
Igniter Failure?

Think I may have found the problem...CkPS was disconnected(?!) The comment by 19963.4lsr5 was right on the money. Thx!


Haven't put everything back together yet, but I'm assuming it will at least run now.

Curious if it will go back to the "shuts off when warmed up" symptom.. Trying to wrap my brain around whether that could have been caused/happening while the connector was partially in place, and will be completely resolved now that it's fully clicked in.

The connector may be broken. I've seen it more than once with those hard to reach wires that they are sometimes forced open and the constant heat cycles weaken the plastic lock tab to the point of breaking. Nothing a zip tie can't solve though. Transmission connectors do this too.

It made a weird brief shriek after the engine caught. Never heard that on either of them before. But, it fired right up and has been running solid (with no shrieks on subsequent starts). So…

Connector was pretty tight. I had to squeeze extra hard to get the click from it. I’m thinking when PO had the “new” 115k engine swapped in they failed to seat it and it just took a while to work out.

Thanks for the support! ~m.