Faultcode 14

[Redvalley]

Hi!

I just bought my first LS400, but I’m having some issues getting it to start.

The main problem is that the fuel pump won’t turn on when I switch on the ignition. I tested the pump by applying 12V directly, and it runs just fine.

I then checked for fault codes and got code 14, which I understand means “ignition signal fault.” After that, I measured pins A14 and A15 on the ECU. On A14 I measured 12V when the ignition was on, which seems normal. However, the readings on A15 were strange.

From what I understand, A15 should be sending a pulsed signal between 0 and 5–12V during cranking. Instead, I measured:
 • 0V before ignition,
 • 10V when the ignition is turned on,
 • then while cranking, it drops to 6V and slowly rises to about 8V and stays there.

I also tried disconnecting the igniter, but I got the same measurements.

Does anyone know what could be causing this?

Thanks in advance!

Kind regards from Norway!

[Jeremy M.]

I've looked online for some wiring diagrams for your model, and found one for a 1993 that should match, but the diagram is incomplete. It does show pin A-15 goes through the kick-down switch for the transmission and then to ground, so seeing voltage there would indicate a short, probably where that wire and at least one other is rubbing into each other and breaking their insulating sleeve. Check your wiring colors, and if they match the diagram I found, trace the harness following the appropriate green/yellow wire, and try to find that short.

If the colors don't match, I would recommend going to https://techinfo.toyota.com and purchasing the 2-day subscription for $25, which will get you access to the correct factory wiring diagrams. If you need help interpreting any of those diagrams, you can post them here for assistance.

[RX400h06]

It sounds like you're diving deep into diagnostics—nice work! Code 14 on the 1992 Lexus LS400 typically indicates an ignition signal fault, meaning the ECU isn't receiving confirmation of ignition from the igniter. Since you've already tested the fuel pump and confirmed it works when powered directly, the issue likely lies in the ignition system rather than the fuel delivery.

Your voltage readings on A15 are definitely unusual. Normally, during cranking, it should pulse between 0V and 5–12V, but instead, you're seeing a steady rise from 6V to 8V, which suggests a weak or inconsistent signal. Here are a few possible causes:

1. Faulty Igniter – The igniter is responsible for sending the ignition confirmation signal (IGF) to the ECU. If it's failing, the ECU may not activate the fuel pump.
2. Crankshaft Position Sensor Issue – If the crank sensor isn't providing a proper signal, the ECU may not trigger ignition properly.
3. Wiring or Connector Problems – A loose or corroded connection between the igniter, ECU, or crank sensor could cause erratic voltage readings.
4. ECU Malfunction – While rare, a failing ECU could result in incorrect voltage signals.

Since disconnecting the igniter didn’t change your readings, it might be worth checking the crankshaft position sensor and its wiring. Also, inspect the igniter connections for corrosion or loose pins. If possible, swapping in a known-good igniter could help rule it out.

[Redvalley]

Thx!

I will have a check on what you guys have suggest! The car have not been on the road for the past 10 years so a bad connection is not impossible, can a bad grounding also give me readings like this on the ECU?