My 2010 Honda SH150i Scooter wouldn’t start after a long ride, but then it restarted in the morning.

[Elvis]

Quick Synopsis: If your SH150i won’t start after a long ride, but can start up hours later, it could be a simple case of your coolant level being too low, causing the bike to overheat.


The Scenario: I rode my 2010 SH150i for about 45 minutes. A couple hours later it would not start; the yellow PGM-FI light would not come on when I turned the key, and I did not hear the 2 seconds of whine from the fuel pump running. I had the bike towed home. But when it arrived home, it started up. (The PGM-FI (Programmed Fuel Injection) light is also called the MIL (Malfunction Indicator Light). It's the yellow light just above the speedometer, with what looks like a car engine icon, like the “check engine light" on a car.)

I thought it was likely the Fuel Pump having an intermittent problem, so I replaced it. The bike seemed to be OK for a while.

But then the same thing happened again. So I figured it might be the Fuel Pump Relay.

The bike uses three of the same relay (Honda part number 38501-KVZ-631) for the Fuel Pump Relay, Main Relay and Fan Motor Relay. The OEM relays are only about $10 each at Partzilla.com, so I decided to replace all three, because for a 15 year old bike that would be an inexpensive preventative maintenance move.

The Fuel Pump Relay is located near the tail light, behind the gas tank. You have to remove the Frame Body Cover (page 2-6 of the Honda Service Manual (HSM) to access it.

I also wanted to check the fuse to the fuel pump, so I removed the Front Upper Cover (page 2-10 of the HSM).

I checked the fuel pump fuse in the fuse box (there’s a diagram inside the fuse box to tell you which one it is). The fuse was good. I did a test: With the fuel pump fuse removed the PGM-FI light still came on for two seconds when I turned on the key (but no fuel pump sound).

The Main Relay and Fan Motor Relay are under that cover, behind the fuse box. It’s easy enough to pull up the fuse box, then slide forward the plastic bracket that holds the two relays for access.

The relays are a little tough to pull out; I had to wiggle them from side to side and back and forth.

I did a test: I found that even with the Fuel Pump Relay removed, again, the PGM-FI light still came on for two seconds when I turned on the key (but no fuel pump sound).

I applied Silicone Dielectric Grease to the prongs of the new relays before I installed them, to prevent possible corrosion and also make them easier to take out next time.

While I had the Front Upper Cover off, I noticed that the coolant level in the translucent white coolant tank was at the line for the lower level. I then took off the radiator cap and had a big surprise: I could not see any coolant in the radiator! It was empty!

I then understood what probably happened. The bike had overheated, so the ECT (Engine Coolant Temperature sensor) had told the ECM (Engine Control Module) that it was too hot, so the ECM shut down power to the FI system until things cooled down. That would explain the intermittent shutdowns I’d experienced.

(Apparently it is the ECM that supplies power for 2 seconds to the Fuel Pump Relay when the key is turned on.)

I filled the radiator and coolant tank / system as per the HSM. It’s only been a couple days, but after one long ride, so far so good!

It’s important to note that I did not notice the coolant being too hot when the bike shut down after a long ride; the temperature gauge didn’t indicate that. There were no warning lights that came on.

I learned my lesson: Check the radiator level every couple months! Don’t expect the instrument panel to tell you it’s low on coolant.

Happy Scooting!