ls40098

Hello all, not sure if anyone can help but here goes….
Sub zero here…battery goes completely dead. Half frozen I get a boost…wrong polarity and blew the 80A main fuse. Having done this before, I did have a spare. Replaced it, dash lights etc come on.

Problems experiencing now…..

Initially very hard to start…eventually did run.

Idles quite fast now…1000-1100

When pressing gas pedal, nothing until almost to floor, the will rev.

When engaging from P to R or D a hard shift due to high idle is my guess.

When driving after fully warmed up, very hard first shift at 2200, hard again at around 3200, definitely not shifting higher.

Last thing..no cruise light comes on at all when pressed button on stalk.

Any help or suggestions greatly appreciated.

tia

mnewxcv

its tough to say if those are all related to the fuse blowing. some of the issues(high idle hard shifts) could be because the battery died and the computer has to relearn. Also could be due to sub zero temps.... hope someone else has more insight for you though.

ls40098

Thanks , I have the battery on charge and its still showing low. I'm hoping driving will help but don't want it blowing up either!

Sub zero is putting it mildly with colder on its way tomorrow.

Yamae

Sounds like a partially damaged ECU or some more blown fuse to me.

When the low impedance of reversed voltage is applied to the battery, it takes several milliseconds or more to blow the fuse. During that time period, the ECU and other equipments connected directory to the battery only via fuses receive the negative voltage. This causes damaged semiconductor(s) or blown fuse(s) some time. Many equipments have protection diodes at the input circuit but they are not always perfect.

Judging from your symptom the processor is still alive but the memory is partially erased or dead or simply some more fuse(s) might blown.

Check other fuses and try resetting the ECU doing as follows.
1, Disconnect the negative battery cable for 5 minutes with head lights switch On.
2, Connect the negative battery cable for 1 minutes with head lights switch Off.
3, The same with 1.
4, The same with 2.
5, Start the engine and run ( if engine runs better) for a while.

If above does not improve the situation, try 1-5 again, If the 2nd try is not effective, you probably need to fix the ECU.
The reason to turn the headlights switch On is to discharge the remaining energy quickly.

ls40098

Thanks for the detailed reply, I will do try that sequence and hope for the best!

MistaG1

I was experiencing the same issues with idle...LS4 seemed like it wanted to cut off while stopped at a light...had diagnostics done and they said I needed converter...I replaced converter and had same issues. Currently having new plugs and wires put in. Hopefully this will fix but if not, you bring up a point in checking the fuses.

Thanks

ls40098

Update!!

Checked all fuses now that it is daylight again, Fuses for radi and ECU were blown. Replaced and all is well for what I can tell.

Cruise is back.
Acceleration is normal
Shifting normal

Thanks for those who responded.

Yamae

Congratulations on your success. I'm glad that you made it.
Be careful when you boost next time.

fixmiester

I'm surprised that it ran at all with a blown ECU fuse; is that by design?

Yamae

Yes, that is by design.Toyota calls it a robust design. The ECU is tested many times applying the negative voltage at the design stage in order to confirm that the ECU can withstand it. Toyota requires this and engineers need to work harder.

There is a big diode that bypasses/clamps the current when negative voltage is applied to the ECU. There goes too big current to the diode and the fuse is blown. But there exists a forward voltage of about -0.7V and also it takes several milliseconds or more to blow up the fuse. These sometimes causes a problem but it is not often. In order to minimize the problem, studies, calculations, selections of parts and experiments are done extensively. I think I was a bit tired of doing those.

mnewxcv

good info, though he is saying that the car starts runs and drives with a blown ecu fuse (no power to ecu?), not that it can withstand negative voltage.

Yamae

There are 2 different 12V supplies to the ECU. One is via the ignition key switch and the other directory to the ECU. Of course there exists a fuse at each line. The blown fuse was at the latter one. The latter one is mostly for the back up of memories. The former one is for processors, sensors and drivers. I think this is enough for you to understand.

LScowboyLS

A person is very lucky if he can install the battery terminals or jumper cables backwards and get away from that error with only fuses to buy - usually you ruin components

Please be very careful when hooking up batteries and jump starting, it can be very hard on your wallet!

ls40098

Totally agree, when you think about it, the the stress of wondering what was wrong, standing in sub zero temps while snowing to change out the main fuse......all for not taking another second to make sure the cables were connected correctly.

A smart car too...the horn blasts as soon as the cables are incorrectly attached. At least it warning you that bad things are about to happen.

thanks again guys, learned alot!