Problem with EV Mod.

Assuming you are using the Coastal Tech unit:

The obvious thing is to check all your connections, with a meter if you can. Also with the meter, you can check whether the orange wire is getting grounded when you pull on the stalk.

If that checks out, the unit may be defective. CT will send you a new one, if you can get hold of them (try phone, they don't answer emails). I've been through three of them, and then gave up.

Finally, there can be a problem with the car. There appears to be one with mine: using a direct switch I can get EV mode, but the car does not signal whether it is in EV mode.

 

Is the EV battery fully charged? The EV unit is very careful about not engaging unless the EV battery is in a high state of charge. Quite often, the unit does not work when I first run the car, presumably because the battery has to be 'topped off' after resting. But while driving (under 34 mph) when fully charged, a lengthy pull on the stalk engages it.
BTW, if I had to do it all over again, I wouldn't. The limitations (battery capacity, safety re battery rundown, acceleration and speed cutoff) limit its utility (it disengages) to the point where it's just a bit of a parlor trick. And I don't think that it's the fault of CoastalTech. It's the inherent design of the Prius' electronics and electricals.

 

I have a factory EV switch - all European Gen 2 cars were fitted with them. Your description is exactly the same (except the UK limit is 29mph, not 34), and yes, I agree that the EV switch is mostly useless. It's nice when manoeuvring a short distance at low speed, for example to let someone else out of a parking space.

The switch is just a momentary switch - the HV ECU has all the logic. CoastalTech's kit is there to repurpose an existing lever, rather than install a new switch, but any press-button switch that contacts the correct terminals does the job (and is more reliable). The factory switch is a bit out of the way, being down and to the side of the steering column.

 

I disagree, but maybe it depends on where you drive. Yes the amount of EV distance is severely limited by capacity of the battery, but I use mine in several places. One is a 25 MPH road with a 4 stop signs. Mostly 150' to 200' apart, one set is no more than 50'. Stop, start moving and unless you are VERY gentle, the ICE kicks on. So I engage EV as I come to the first stop and disengage either as I approach the signal at the end of the run (if Green) or when I leave the red light. Forced EV is MUCH less sensitive to reasonable acceleration than auto EV. Another section (30 MPH), the car will sometimes do auto EV and sometimes not. I force EV once I crest the small hill if it doesn't go to auto EV. The 2010 will fail here since EV cuts out over 25 MPH. Another section, again 25 MPH - on the way TO work when the engine is warm, I can make the entire mile on auto EV if the battery starts at or above 6 blue bars and not go below 4. On the way home, it might not go into auto EV (due to slightly low engine temp) so I will force it. I NEVER force it, or let it drop while in EV, to less than 4 bars. It will kick out at 2 bars but I see no reason to push it that far.

And as you say, it is the 'fault' of the Prius design, not the implementation of engaging it.

 

I installed the Coastaletech mod in my 2005 Prius today. It worked wonderfully the first two times I engaged it. The third time, with the battery in the green, I could hear an airflow noise coming from the battery vent to the far passenger side of the back seat. I've had the Prius for two years and have never heard that before. Has anyone else ever heard that ventilation sound?

Also, the EV mode won't engage anymore. Ever since that vent sound (which only happened once so far) I get three beeps when holding the stalk forward, as if I'm disengaging EV mode. It never engages now. Any tips?