gx4702005b

I have a Lexus gx470 2005. it starts whenever it feels like starting (whenever I see the check engine light in the dash the car starts perfectly fine) and I can drive it for 5 hours with no problem and then sometimes I come back to the car and the check engine light does not light up when turning the key and it does not start, no crank no start plug in a scanner no connection to ecu. brought it to a mechanic shop that specializes in Toyota. they told me to buy a new ECU 400$ later gave me the car today saying the problem was solved I went pick it up and parked it at my house, I came back 1 hour later and the same story. no check engine light no start. I already checked all the fuses and relays all of them seem to work. I ran out of ideas. please help

LeX2K

Is there a relay marked EFI? Sometimes they go bad and when they do you get a crank no start and no check engine light.

gx4702005b

already checked the EFI relay and changed it with another relay with no luck.

LeX2K

Do you have power at the EFI relay? Both power to the relay coil and power to the relay contact pin. Pull the relay in and out of the socket with the key to ON it should click.

gx4702005b

yes, i just went and checked. the relay clicks when you take it off and put it back on

Margate330

If someone has the electrical for the ecm this riddle can probably be solved quickly.
Only thing is to be careful when checking voltage at the ecm- it's easy to bridge/short connections when back pinning the connectors.

gx4702005b

I hope someone can help I already spent too much and just did a full timing belt kit on it too. so everything is adding up

LeX2K

Need a wiring diagram, anyone have? Is there a security light in the cluster or near by? And if so does it go out when you insert the key?

gx4702005b

yes the security light flashes when the key is not in and then when i insert the key it goes away

LeX2K

That's a good sign means the security system is not locking you out. You need some basic troubleshooting tools like spade leads/wires to insert in place of the relay, a test light, volt meter. Another way is to get a spare relay and remove the plastic cover so you have test points.

Hope someone can post a wiring diagram. The service manual has a list of voltage checks you can do right at the ECU. When the truck was running, did you see the check engine light as you started the car (goes out of course after a few seconds). Want to make sure the light is actually working.

chiph9

Check out the diagrams in the sticky post above, titled "GX Wiring Diagram Engine Control"

Chip H.

gx4702005b

I can not seem to find the diagram to check the ECU. I just checked all the fuses today and all of them seem to be working properly except 2 of them that did not light the tester up.
Fuses are STA fuse
and ST2 fuse
both underneath the steering wheel fuse box.
I checked both of them and they are not blown. plugged in a spare fuse but did not light the tester up either. should they light up if the car is with the ignition in the on position?
thank you in advance for helping me.
Also I removed the whole glove box to get to the computer but do not know how to test if it is working or not.

dorgknorl

I an having exactly the same problem on a '06, also with recent timing belt change. Seems the only interface with the electronics during that procedure is the cam sensor and the crankshaft sensor. I torn mine back to those connections and checked them, with no success. During this time the car also had the fuel pump resistor fail, the car would start but stop as soon as the key was back to on. First the resistor was shorted, which made it run correctly, then the resistor was replace. Now won't crank (with or without resistor shorted). Only other change from normal was the connection of a trailer with brakes. Towed two miles then these problems started.
After the cambelt change it ran fine, even though the timing was off. That was corrected by rolling a 1/4 inch extension between the belt and the right bank gear, as suggested elsewhere on this forum. The car ran fine until the trailer was connected.
All fuses and relays test fine and the starter cranks when the relay is jumped.
So, there is an open somewhere. When removing the glove compartment to check for water damage (there is none) a large rats nest was found above the cabin filter. No indication of damage in the wiring at that location.
There is no voltage drop between the battery and the fuse/relay box under the hood. A jumper cable was connected between the engine and the battery, to no avail, so the engine ground is good.
Short description of problem: good battery and connections, but no crank in park or neutral and no check engine light with key on engine off.

Update:
2/4/22
Finally got this vehicle to run and it ran perfectly on first crank. I arrived at the solution after hiring a mobile technician to help identify the problem. He got stumped, but did diagnose that there was no voltage on the can bus at the dlc port. He determined that there was continuity between the dlc port and the ecm. He had never heard of that before and was stumped. That evening, using a google search with the question no crank no can bus voltage at odb, the following video was found: . The next day the left cam sensor was disconnected (because it was involved in the cam belt change and has a wire that could be interfered with by the rotating assembly.) The engine would crank but not start. The cam position sensor was removed and the wire was damaged. The cable from the cam position sensor to the connector has three wires and a metal cable that is grounded to the sensor, presumably to stiffen it. The cut in the cable on this vehicle caused a short from the black and red wires to this grounded cable, taking down the can bus. Upon repair and reassembly the engine ran perfectly.