Approximately two months ago, my 1990 LS400 would not start. No codes came up. I did basic fuel and spark trouble shooting and traced the problem to weak spark on the left side. The right side was not great either but passable. I had recently done wires and plugs so I went a bit deeper and replaced the distributor caps and rotors. The old ones showed a lot of carbon tracking. The cam position sensors looked pretty good and tested ok so I just reused the old ones. I also took the time to replace my thermostat to fix a pesky leak from the thermostat housing. While I was there, I also replaced my engine temp sensor. So I was back in business and the car was running better than I could remember in a long time.

Fast forward to last Wednesday morning and she wouldn’t start again. Luckily the old girl was polite enough to take a vacation in the garage for a second time rather than on the road somewhere. Again, I had no OBD codes and no clue what the problem might be. I did the quick fuel check and that looked ok. I had just done most of the ignition system so I didn’t think that was the issue. And I didn’t have anyone handy to crank the engine while I checked for spark. So I poked around looking at everything else to see if I could find anything obvious. It still would not start - but now I was getting a code 24 leading me to the intake air temp. It tested ok though.

Finally my wife came home and I asked her to crank while I checked for spark. Bingo. No spark at all on either side. Completely dead. And, I was now getting a code 12 for the RPM signal at the ECU. I’m not sure why I hadn’t gotten a code 12 before but now I had something to go on.

The next morning I pulled the crank position sensor. It was caked with crud on the sensor end and generally covered with grime (see picture). And it tested completely open circuit. I’m thinking that the leak that I had from the thermostat housing had run down the front of the engine into the lower engine front cover and fouled to sensor.

I was able to track down a replacement at AutoZone for $79. Sewell has them for $115 and my local dealer wanted $204. The one I got from AutoZone was a Denso stamped with the Toyota name and the same Lexus part number as the one that came out (90919-05002). The sensor is located on the driver side under the crank pulley. If you take off the engine under cover, the sensor is right there and easy to R&R with just one 10mm bolt.

So don’t let a leak at your thermostat housing go for too long or you could have the same issue. Hopefully this write-up will help someone down the road.

 

Great info! Having previously owned a 7.3 Powerstroke, I am very familier with these.

 

Although you have some coolant and dirt on that sensor it also looks like you have some oil on it. Do you have any signs of oil leaking out the bottom of the lower timing cover? It seems to me that your crankshaft seal might be leaking. My crankshaft sensor had oil on it (not as bad as yours) when my seal was leaking. If it leaks bad enough the oil can get on the timing belt and might either weaken the belt or slip and jump time. Take a look at it when ya get a shot, it might save you some trouble in the long run.

 

Thanks deanshark for the heads up. When I did the distributor work I had the top T-belt covers off and took a good look at the belt. It looked pretty good with no signs of oil contamination. And when I took the crank sensor out, there was gunk caked at the top edge of the hole. I used a 90* dental pick to carefully clean what I could from up there. Everything that came out was a bit moist but not wet and oily. That’s what made me think that coolant had been pooling down there and then the residue started to dry when I fixed the leak a few months ago.

BTW, with the new crank sensor, the engine starts after about one or two turns now. No more cranking for a second or two. Man, what a difference.

 

I think I might have the same issue in my 95 Sc400 1UZ. No spark on ether side.
Could you explain how to test the Sensor before I go hunt one down? Thank you!

 

Even if its okay, if you plan on keeping the car it will go out someday, then you will have the replacement on hand.

 

Sorry for reopening this post, just found it via Google. Can you tell me a location of this sensor (picture would be highly appreciated)?

Thanks in advance!

 

Access from underneath, it points up at an angle, approx 10 o'clock, at the position plate which looks very similar to a small bicycle sprocket.