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I recently bought a 93 Lexus ls400 thinking it was just going to be the ignition coil, I parked it for the night then came out the next morning going to install the coil and it wouldn't crank but battery is brand new, everything has power and relays are energizing but no crank. I replaced the starter thinking that may be the issue along with the relay, no resolve. Tested everything with a voltmeter and still got proper volts. Just pulled ECM out and everything looked good inside and the past owner actually replaced in 2014. I'm drawing blanks but may go tomorrow and get a new key cut from Lexus. Any help or advice would be great, Thanks in advance!
It did turn over when I jumped the relay but but no crank.
turning over and cranking generally mean the same thing
Another thought popped into my head. Is your ignition switch working correctly? Have you verified that the wire that sends the 'start' signal makes contact when you turn the key to start?
I honesty don't know how to test the ignition switch, I was even thinking about running a push button lol. And if your talking about the starter wire it is in good condition
I honesty don't know how to test the ignition switch, I was even thinking about running a push button lol. And if your talking about the starter wire it is in good condition
There are two starter wires; a thin one that energizes the solenoid plunger (when the key is turned all the way to 'start') and a big thick one that's always on which goes to the starter motor itself. Are they both good?
I recently bought a 93 Lexus ls400 thinking it was just going to be the ignition coil, I parked it for the night then came out the next morning going to install the coil and it wouldn't crank but battery is brand new, everything has power and relays are energizing but no crank. I replaced the starter thinking that may be the issue along with the relay, no resolve.
Was it running when you bought it, but running bad? Is that why you thought a coil, no spark?
Do you mean the engine wouldn't turn, or it would turn but not start? You might have set the alarm ( immobilizer) somehow. If you turn the key and have power to everything but the engine wont turn over, (crank) try unsetting the alarm by unlocking the passenger door with the key twice.
Was it running when you bought it, but running bad? Is that why you thought a coil, no spark?
Do you mean the engine wouldn't turn, or it would turn but not start? You might have set the alarm ( immobilizer) somehow. If you turn the key and have power to everything but the engine wont turn over, (crank) try unsetting the alarm by unlocking the passenger door with the key twice.
I tried to unlock it and it didn’t work either and apparently the 93 doesn’t have an immobilizer. And it won’t turn at all unless I jump the starter relay against the positive battery terminal and even then it just cracks over no start. I bought a alternator today and a key switch is supposed to come in Monday so hoping it’ll work, pray for me lol
I tried to unlock it and it didn’t work either and apparently the 93 doesn’t have an immobilizer. And it won’t turn at all unless I jump the starter relay against the positive battery terminal and even then it just cracks over no start. I bought a alternator today and a key switch is supposed to come in Monday so hoping it’ll work, pray for me lol
When you do get it to crank over but not start, have you checked to see if you're getting spark and/or fuel? I'd think you would at least first check for spark before throwing unnecessary parts at it. Good luck.
When you do get it to crank over but not start, have you checked to see if you're getting spark and/or fuel? I'd think you would at least first check for spark before throwing unnecessary parts at it. Good luck.
I saw that thread. I have a '91, which is what is discussed there. I think that even if the ECU or anti-theft system wants to stop the engine from cranking, it can be easily bypassed at the starter relay, which OP says he has done.
From the circuit diagram I found (not sure of year), the connection between the ECU and starter relay is shown. In addition to any starter blocking, that may also be for ECU monitoring, allowing it to control the fuel pump, including running the pump when the starter is engaged. If the starter relay is bypassed (easily), there is no alarm / ECU / immobilizer that should stop the engine from cranking. Actually starting is a different issue of course.
Here's a pic I found. NOT SURE WHAT YEAR! I could not find my own circuit diagram. From memory, it seems to be the same as my '91. But it shows how simple it is going from the battery to the starter.
Basically, the black-blue wire in the lower left is the thick wire where the 400 Amp (or whatever it is) current flows to spin the starter. Direct from the battery. Live at all times at the starter. No fuse or anything to stop it. The "starter" rectangle includes the starter solenoid, which controls the current to the starter, and is itself controlled by ...
The red wire on the left side shows how the battery connects through the relay and solenoid to control the starter.
Starting up in the upper right shows where the ignition switch, when turned to the start position goes through a 7.5A ST fuse (see below - I had a problem with that once) to trigger the starter relay, which has its own 40A fuse. With the starter relay triggered (or jumpered), the 40A-limited current should flow to the starter solenoid, which should throw that mega-switch, engaging the starter gear (Bendix) with the flywheel, and allowing the hundreds of Amps to flow through the starter, cranking the engine.
The Neutral Safety Switch (labeled Neutral Switch in the diagram) is a not-uncommon point of failure here. It won't let you crank the engine unless you're in P or N, and sometimes even when you are in one of those, a failed NSS will think you are not, preventing the start. More specifically, it prevents the starter relay from triggering. But if you bypass that and still have a problem, it is not the NSS. The first easy test is to see if you can start in N rather than P.
At a basic level, the starter system is pretty simple. Apply voltage (with enough current behind it) to the starter, and it should engage the flywheel and spin the engine. Easy to analyze the circuit and jumper past any points needed to get the starter powered. I once had a blown 7.5 A "ST" fuse in the driver's footwell fusebox that led me to jumper the starter relay in the engine bay fuse box until I tracked it down.
I would not have replaced the starter (as a reader on here, I know that is not a quick and easy job) without carefully analyzing everything in the circuit to confirm a bad starter. And just because the starter is new does not mean it's good.
At this point I would test the whole circuit, making no assumptions about what is good or not. It's a simple circuit.
And here, I just found a scan I made from my wiring service manual, which is for my '91. Interesting how it looks different from the one above, but without studying closely, I think it's a very similar circuit. Probably helpful to have both, and know that this one is definitely for the '91 (and not sure about other years). The colored version in the previous post may be more useful for general understanding, but if you want the absolute correct details, this one here is it, for '91.
07-08-19, 05:42 PM
93 LS400 no crank, spark, or fuel
