2008 Prius won't start intermittently

mjm2008,

My take on this:

Check the tightness of the connection of the wire "grounding strap"
between the 12V battery and the chassis. It's back under the
passenger side tail light. You have to lift out the hatch area floor piece
and the tray underneath. You also have to remove the small, roughly
triangular floor piece on the passenger side.

The wire is the black one with the white tape holding it in an arc on
the right top in this picture:


Also check to tightness/snugness of the connections at the +/- battery
lugs.

As to the new 12V battery; I'm wondering if the ground has been/is
intermittent, could there be a chance that it has not been recharging
fully?
(And this could have been the basis of the need for the new battery?)

With luck one of the e-smart members will post up on this.

 

I think the brake light switch needs to be adjusted or replaced.

 

I was going to make the same suggestion Patrick did. I also think that checking the ground cable at the 12v battery is a good suggestion.

 

Hi Patrick, I thought the same, but then I went out and turned my 2007 Prius on and off a few times, and discovered that the ready icon first does one very quick blink before lighting steadily. So that may be normal, but we just never noticed before, because it does it in the blink of an eye, so to speak.

Or could there be something wrong with my car that I haven't noticed?

 

Hi Fred,

You are right, I noticed the one blink of the READY icon on my 2007 this afternoon. I agree that this blink is normal and I corrected my earlier post.

Regarding the OP's hearing relays clicking, perhaps s/he is hearing the three system main relays. When the car is started up, two of the relays energize, to connect the negative and positive battery terminals to the traction battery cable that runs up to the inverter.

A resistor is connected in series, in the positive traction battery line. The resistor reduces current flow as the inverter capacitors charge up. A brief moment later, the third system main relay will energize to bypass the resistor and allow unimpeded current flow to/from the traction battery.

 

Thank you for confirming that for us!
Funny that we never noticed during years of driving.

IIRC those relays are located inside the HV battery casing. So those clicks would be the more muffled sounding ones coming from the back of the car. They also sound a little different when powering down.


Another little tip for the OP: If you drape a towel or something over the middle of the rear spoiler so that you can see it through the little lower rear window, then you can easily see if the brake switch is working. If you can manage to observe the brake light every single time you power up, then the next time you have a start failure, you will know if it was because of the brake switch or not.

 

I think I recall someone saying (Patrick?) that the brake switch has two poles, so it is (just) possible that the pole switching on the brake light works while the one needed for the starting interlock isn't working. On the other hand, if the brake lights don't come on, that's likely the problem.

 

Gen II Prius with Cruise Control have two poles on the switch. One runs the brake lights and starting interlock, the other disengages the CC.

Tom

 

The switch is located near the brake pedal lever pivot point. The clearance between the switch and the lever should be 0.5 - 2.4 mm. The lock nut tightening torque is 19 ft.-lb.