Unable to start - 12V battery OK

Looking for some help please before I give the car to a dealer to fix.

This morning I couldn't open the drivers door with the remote, so I used the key and got in. No alarm went off, dash was blank, no beeps. I held the key fob up to the start button - nothing. I opened the rear passenger door and folded down the rear seat to get to the 12V battery, this checked out fine with 12.7V.

I checked some fuses under the bonnet these were good, I looked for the fusebox in the car but being a RHD model this is in the passenger footwell and hard to access so I didn't check any of them.

I googled up jump starting a Prius and found this:

I found the jump start terminal in the fusebox, this had something like 40mV so I gave up and called the breakdown service. An hour later they came along and hooked up a big battery to the jump start terminal, the car could then be started up. We left the engine running until it warmed up and cut out, then the man disconnected the starter battery and the car carried on in Ready mode, lights fan etc. all OK, but rear hatch wouldn't unlock. I switched the system off then everything died again, no lights etc.

He then reconnected the battery and car started again (ie went to Ready, engine didn't need to start as main battery showing 3 bars). He said he couldn't fix the issue and I should take the car to a dealer and drove off.

I then shutdown and had lunch, after lunch I tried same trick of connecting 12V to the jump start connector but it wouldn't have it. I tried various power sources - 12V 1A power supply - over load. 12V 2A power supply - showed 5V @ 2A overload. I tried a small 12V battery charger - this blew its 5A fuse. I tried jump starting from a Ford petrol car connecting jump leads to its 12V battery whilst engine running - still no start (no idea how much current it took).

I am guessing a fuse has blown, maybe an issue with the central locking shorting out, but now I am unable to start the car to drive it to the Toyota garage (10 miles away).

Any suggestions please, particularly simple things like fuses? How for example is the 12V battery connected to the main system? How much current @12V does the jump start terminal need if the 12V battery is disconnected?

Regards,
John

 

Just rechecked, this time I read 2.3V at the jump start terminal to the engine bolt, a bit higher than 40mV read earlier. I agree there does seem to be a disconnect somewhere.

Regards,
John

 

I found a picture of the 140A aux 12V battery fuse here:

http://priuschat.com/attachments/p6031322-jpg.52571/

I will check this tomorrow (it's night time here now) and report back.

Regards,
John
PS The 12V battery is original, but I guess as it is now 7 years old it is due for replacement.

 

OK - a bit of history on the car, may or may not be relevant to the 'no start' problem. About 4 weeks ago I damaged the rear bumper (reversed into a wall), and had a new bumper fitted (insurance job - had to pay an excess). The repair garage also had to replace a metal bracket that ran along the back of the car. I think they removed or disconnected the 12V battery when doing the repair. Maybe the battery was damaged in the accident or not refitted correctly. Anyway the repair garage gave me a 12 month warranty on their repairs which may be useful once the root cause of the 'no start' problem is found, or might be part of the insurance claim if in that area (and not the battery itself which won't be covered). The car ran fine after the bump and after the repair, but maybe something electrical in the boot area was weakened.

Looking at the photo of the 140A fuse I guess if open the whole black part fitted with the two bolts will need replacing. I will test voltages then assuming it is not 0V across the fuse I will assume it is faulty.

Also, what is the grey part between the black fuse and the battery + terminal? Another place where an open circuit could occur I guess.

Regards,
John

 

Update for Sunday morning - looks like a faulty ground strap on the 12V battery.

I first checked the voltages around the 12V battery. Black lead of meter on battery negative post, readings were:
- battery positive post and both bolts on the 140A fuse = 12.7V

Therefore 140A fuse is showing 0V across it ie good.

I then checked in the engine compartment, black lead of meter on big bolt to left of engine, jump start terminal = 2.4V.

Back in the boot I then had the idea of measuring voltages relative to the luggage tie bolt, so with black lead lead of meter on the luggage bolt, battery positive post = 2.4V, battery negative post = -10.3V.

I then found a long lead (black jump start lead plus another short lead) and measured from the engine compartment (black lead on big bolt), again battery positive post = 2.4V, battery negative post = -10.3V.

So looks like a good connection between battery positive and jump start terminal in engine compartment, which I thought was the problem last night, and a poor connection between the battery negative and car chassis, which I had assumed was good.

I haven't opened the boot as this is controlled by central locking (dead) so will try the manual route in for more checks.

As the ground strap was one of the places where the repair work was done I will get onto them on Monday, luckily the repair shop is only a mile away.

Regards,
John

 

Here's the errant ground strap (excuse finger!). Looks in good shape, clearly not making electrical contact with the chassis. I picked up the repaired car on 12th Aug so I don't know why it ever worked.

Please can someone confirm this is the right bolt hole?



Here's the inside of the boot from the back seat:


The latch to open the hatch is easily accessible - there is no cover fitted. All I have removed this picture is:
- battery cover
- shelf and under shelf storage tray
- trim behind battery

Should there be any other trim on a UK Prius, (if so photos please), there is no cover to remove to access the hatch latch like there is in the US Prius,

Off to complain to the repair company on Monday, hopefully a good chassis connection will restore normal operation,

Regards,
John

 

Thanks to IMkenNY! I tightened the chassis bolt by a quarter turn and the interior lights and dash display came on, a further quarter turn to make it really tight.

The car was stuck in 'On' mode, ie same as press power twice without depressing brake pedal. This is quite a high drain mode so the poor earth added several ohms of resistance, causing a 10.3V drop between chassis and battery negative leaving just 2.4V to try and power up all the accessories.

I pressed power to switch the car off, then power twice to put in On mode, all OK no warnings, pressed brake and power to goto Ready mode, all good and main battery showing 4 or 5 bars. Went for a 10 minute drive and turned off, battery measured 13V across its terminals. Restarted fine and now all back to normal - no need to go back to repair shop and lesson learned to check the basics such as having a good earth to battery negative.

I will keep an eye on the 12V battery, it is really warm here this summer (20C high, 10C low) so battery should last until winter.

Thanks again for help and for reading my ramblings!

I am still unsure if any trim has gone missing from the boot (trunk), so will look forward to any photos.

John