My Honda won’t start when hot
To diagnose a No Crank When Hot – Honda, or engine is hot, take a look at this diagram. Battery voltage flows through fuses to the ignition switch. When you turn the key to start, contacts in the ignition switch close and send power to the starter cut relay (located under the dash in the fuse/relay box). The voltage energizes the relay coil which eventually pulls in the contacts, sending voltage to the starter motor solenoid.
However, before the relay coil are energized, the relay coil must find ground through the clutch interlock switch or the transmission range selector. These switches are commonly known as “neutral safety switches” so you cannot start the vehicle while it is in gear. Once the relay coil gets ground, it flow voltage to the starter solenoid coil. That pulls in the heavy duty contacts to connect battery power directly to the starter motor.
When a vehicle starts cold but will not crank when hot, you have to look for those items which might be affected by heat. Obviously, the starter motor solenoid can get hot since it’s connected to the engine.
So check for battery voltage on the black/white wire while the key is in the start position. If you’re not getting voltage at that wire, you’ll have to backtrack. In an automatic transmission vehicle, the transmission range selector is usually mounted on the transmission near where the shift cable attaches to the transmission. So check for voltage on the light green wire with the key in the start position. If you have a manual transmission, check for voltage at the clutch interlock inside the vehicle with the key in the start position. If you still don’t get voltage, jumper across the relay contacts at the starter cut relay in the under dash fuse box. To see a wiring diagram for a standard ISO relay, click here.
© 2012 Rick MuscoplatPosted on by Rick Muscoplat