AHC fuse blowing

[AtinLango]

Recently, there were some rats in my car garage. They entered the bonnet of the landcruiser and visibly chewed some soft cover parts.

Now, two days ago, the AHC OFF light started blinking when i started the car. Upon checking, I found the AHC fuse in the engine bay blown.

I have tried to troubleshoot with my limited knowledge and a basic multimeter. My aim is to look for a short in the AHC wires.

So far, I am not succesful. I also tried by unplugging the connectors to AHC pump motor and AHC height sensors in turn. In each case, the fuse still blows upon starting car.

I am continuing to think through, but i need some ideas on what other tests I can safely try without any risks. I first want to try before i call a wiring technician. There is still some fear lingering in my head given that recently a wiring technician blew my height control switch.

I would appreciate any insights on what tests I can try. Many thanks as always.

 

[2001LC]

Large Rat chewed wires, should be to hard to find.

• First look under the hood. Trace wire back from AHC pump/reservoir. Also wire coming up from front high sensors.
• A common area easily accessed by rodents, is Undercarriage Wiring. In LHD USA models on DS (LH) at rear 1/4 tip. Is a block of wire housing, that come from rear cabin out to undercarriage. The trailer hitch wires come from same block of wire area. The AHC and wheel speed sensors wires, head back toward the front along frame from these blocks. They're hard to see wire, as they go along top of frame at some points. Follow wires, with mirror and flashes light: To AHC rear high sensor, and all globes, the accumulator and controller. The AHC controller, has hard lines and wire harness going to it. It is on inner side of frame, opposite the accumulator under drivers door "A" pillar. Wire come from over frame to accumulator and on to front globe.
• Did they get inside. If so look close under dash and inside of each foot well. The AHC CPU is on DS (LH). A mass of wires head form it and LH junction box. Under and along carpet next to threshold.

 

[AtinLango]

Large Rat chewed wires, should be to hard to find.

• First look under the hood. Trace wire back from AHC pump/reservoir. Also wire coming up from front high sensors.
• A common area easily accessed by rodents, is Undercarriage Wiring. In LHD USA models on DS (LH) at rear 1/4 tip. Is a block of wire housing, that come from rear cabin out to undercarriage. The trailer hitch wires come from same block of wire area. The AHC and wheel speed sensors wires, head back toward the front along frame from these blocks. They're hard to see wire, as they go along top of frame at some points. Follow wires, with mirror and flashes light: To AHC rear high sensor, and all globes, the accumulator and controller. The AHC controller, has hard lines and wire harness going to it. It is on inner side of frame, opposite the accumulator under drivers door "A" pillar. Wire come from over frame to accumulator and on to front globe.
• Did they get inside. If so look close under dash and inside of each foot well. The AHC CPU is on DS (LH). A mass of wires head form it and LH junction box. Under and along carpet next to threshold.

Thanks very much. I appreciate.

I am finding it a little difficult, so i have called a wiring technician. Not sure when he will come over. I will post an update in due course.

 

[AtinLango]

As i wait for the wiring technician, I managed to locate the AHC ECU. I unplugged it. Then started car. The fuse didnt blow.

Does this automatically mean that the AHC ECU is damaged, and is the one causing the fuse to blow?

Are there any other tests that I can do on the AHC ECU?

Some important late finding:
With everything connected, including AHC ECU, but only the AHC pump pressure sensor connector unplugged, the fuse does not blow. And the car rises to neutral height. Though AHC OFF light keeps blinking (understandably because of the unplugged pressure sensor).

What could this mean?

 

[2001LC]

For sure a clue as to which circuit short is on. Did you follow wires from pressure sensors, to wherever they go.

 

[AtinLango]

For sure a clue as to which circuit short is on. Did you follow wires from pressure sensors, to wherever they go.

First, I have ruled out any issue with the pressure sensor itself by swapping with a spare one that i had.

I am now considering probing the wiring between pressure sensor and AHC ECU. Still gathering some courage, especially for fear of damaging some systems.

 

[2001LC]

First, I have ruled out any issue with the pressure sensor itself by swapping with a spare one that i had.

I am now considering probing the wiring between pressure sensor and AHC ECU. Still gathering some courage, especially for fear of damaging some systems.

I didn't think sensor itself, but good you checked. Make sure correct AMP fuse, is being blow. Sometime someone switch in to low AMP. Work for awhile, then blows when system demand more. load.

That fact you mentioned rats. I'd first visually check wires. If you don't find chew/cut/short. Then get out multimeter.

 

[AtinLango]

I have been working with my assistants (Copilot and ChatGPT) to troubleshoot the wiring problem. AHC FUSE blowing everytime I start the engine.

We (I and my two assistants) isolated the problem to AHC pressure sensor circuit. For nearly 2 or 3 full days, we have been struggling to get to the root cause. Sometimes, I have to disagree (respectfully) with my assistants and I reign on them. We always do this since we have worked as partners on a number of projects together, not just car repairs.

Now, we just discovered something after so many tests using my basic multimeter. Long story short ... I decided to cut open the plastic insulator of the 3 wires going into the pressure sensor connector. Upon exposibg them, there appeared to be some cracks in one of the wires, specifically the AHC ECU signal wire. Picture is attached.

I split the three wires apart and plugged in the pressure sensor connector and everything else. I then started the car.

Alas, I started counting seconds and minutes, and the AHC OFF light didnt show. I even cycled heights through L-N-H effortlessly without AHC OFF light blinking.

Now i had to check the condition of the AHC FUSE. It did not blow this time even with pressure sensor plugged in. However, it was a bit hot. Anyhow I had improvised the fuse by bridging with a wire since I didn't have a working 50 amps fuse. Remember I had to blow fuses well over ten times during troubleshooting.

I don't know whether this is a good sign, but i am excited. I want to buy two real fuses and try to see if the fuse heats up.

 

[2001LC]

Good Job!

I'm not seeing the cracks in wires, in picture. But seems you found the short.
Could it be more damage, not yet uncovered, further down sheathing. That just moving wires, help to correct!

I'll add: I had a very strange issue with a 01LX. Where windshield wipers would come on, when it rained or roads wet (snow melt). Strange since the 01LX, did not have rain sensor. It had other issues also, all dealing with wipers and washer. In dry weather things changed. I found rodents had partially chewed through wire(s), up near washer reservoir tank. It seems when wet, it change resistant and voltage jump cross wire.

Repair wires with water tight butt solder

 

[AtinLango]

I have tested again this morning with another bridged fuse. It' remains cold and solid. It's not blowing. The other one that warmed up could have been loose.

I need to quickly get a real fuse today and replace it.

I am still not believing that i found the cause of the problem. But it's definitely working very well now. Atleast I avoided calling a technician who could easily damage my electrical components, like the recent one who burnt the AHC height switch. Moreover they would charge me heavily for their time even if they dont solve the problem.

I will need to get a wiring technician to simply help me insulate the wires properly.

 

[AtinLango]

My car has been running like new since I sorted the fuse blowing issue. The only slight problem was that the front decided to be a bit higher than normal. So i have been struggling to lower it by about 0.3 iches, but all in vain.

In the process, I tried a lot, including swapping AHC pumps (I have 2 of them that i keep swapping when things go wrong). Just yesterday, the fuse started blowing again. As before, the fuse doesn't blow when i unplug the pressure sensor connector. It's like i am back to square one, with the car lying flat in Low and not responding to anything.

The main thing motivating me to try hard until i resolve the issue is the comfort and stellar performance level of the car once it gets to Neutral height. Just yesterday before the fuse started blowing again, it was riding like some kind of aeroplane.

I am back to the drawing board.

 

[2001LC]

Good Job!

I'm not seeing the cracks in wires, in picture. But seems you found the short.
Could it be more damage, not yet uncovered, further down sheathing. That just moving wires, help to correct!

Did you inspect full lengths of wires.

My car has been running like new since I sorted the fuse blowing issue. The only slight problem was that the front decided to be a bit higher than normal. So i have been struggling to lower it by about 0.3 iches, but all in vain.

I

When system working as it should. Position of height sensor, determine height.

Have you read the thread "ABC of AHC". Getting cross leveled, with proper rake (front lower ~.75", than rear) and pressure correct. Along with flushing and making sure no air in system. Is key.

 

[AtinLango]

I got a wiring man. Actually i knew him before but i didnt know he is a wiring man. One time he helped me bleed the landcruiser AHC fluid.

He is simple, very good and very systematic, and communicates and listens very well - exactly the kind of technician I like to work with.

He tried his best and found there was no short. Instead he said it was the motor. That both motors were bad. I have two.

Well, it was a long story. We called the auto shop and they told us a new motor (complete pump assembly) is 2 million shillings (about USD 600). That's the same price I once bought it. We agreed that i look for money this week.

After he left, I went back on the drawing board. I adjusted front sensor voltages and dismantled the two pump assemblies, swapped their motors and re-assembled. The car immediately worked like charm. I went for road test on highway and bad potholes. The car is running perfectly.

But i am afraid. Not sure how long it will last.

I will do some bleeding tomorrow to release any air trapped in during re-installation. I will also borrow techstream to do necessary measurements.

Atleast I have got a good wiring man, hopefully I can rely on him for a while. Meanwhile, my mind is open to buying a new pump assembly.