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Prado 90 Series 1kz Faults - Transmission, overheating, alternator, brakes, suspension, noises & seat cushions


New Member
Sep 7, 2021
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Hi All,

I'm new here. I own a Prado 1997 1KZ with 175,000 km. I am not a mechanic, but I am a bit of an enthusiast. If you are a mechanic please feel free to correct me. I've had a whole range of faults on my vehicle and I would like to take this opportunity to share my findings. I know many of these faults may be common knowledge to some of you, please don't judge me, I am only trying to help.

Fault 1 - Vehicle struggling to climb on steep hills.

On steep hill after/during a long drive the RPM was not increasing and the car would only climb with low range engaged. This fault was fuel related, I changed the fuel filter and this fault was fixed. On another car in the family with exactly the same fault we needed to change the fuel pump aswell.

Fault 2 - ATF Overheating only on hills

This was a tricky one. 1st step check the colour and level of your fluid. It should be red and should not smell burnt. For checking the level, there is a process, I'm sure someone else can post it here.

In my case the ATF was black and lumpy. Now I was faced with a complete transmission flush or just changing the fluid. I chose to just change the fluid, as at this point I was unaware of what exactly caused it to burn. After changing the fluid I then did some research on exactly how the ATF is cooled.

The 1kz ATF is cooled via the radiator. I arranged for the radiator to be flushed/serviced and water replaced with coolant. There was indeed a blockage in the radiator which was cleared.

On my next drive the ATF overheated again. To make matters worse the head gasket blew the next day. The thermostat did not show overheating at any point and ATF has its own warning light.

The radiator fan is belt driven and I could see it turning. It turns out the fan comes with a silicone oil inside, which makes it turn at the correct speed to prevent these faults. The oil dries up over time and needs to be re-filled. There are loads of videos online showing you how to do this.

It also turns out the car thermostat is pretty rubbish. I would suggest you install a separate gauge to measure AFT temp and engine oil temp. There is also the option of installing an additional external cooler, but I personally prefer to get the factory systems working correctly first.

Fault 3 - Car vibrating excessively on the motorway

After fixing all of the above, we had a flood. The car was submerged for about 6 hours in about 3 feet of dirty water.

In Pakistan, when they wash cars, they also spray the bottom with diesel to give a clean and shiny look to the undercarriage. DO NOT let them do that.

Pretty much all of the suspension, steering, struct ect have rubber bits and they all diminish over time. The diesel only accelerates the problem. So if this happens, take the car to a mechanic and be prepared for a big bill.

In my case I also needed a new/nearly new power steering rack

Fault 4 - Wheel falls off while driving

This didn't happen to me, but is worth mentioning. The lower ball joints must be checked regularly and even more if you are off-roading. If one fails, your wheel will fall off.

Fault 5 - Batteries go bad quickly

You probably need a new alternator. In my case some genius decided to put on 300W HID / BiXenon Headlights. Here is a free bit of advise:

If you buy a brand new car with HID lights, you will notice small washer jets on the bumper. In the case of older cars, they had small wipers on the light. This is because HID is a gas ignition bulb that cannot see past dirt. LED does not have this problem. So if you want to change your bulbs, lets face it the factory bulbs are rubbish, please go for LED. This is for two reasons:

HID is no good on a 1997 Prado

Your factory alternator was not designed to handle that kind of load.

Fault 6 - Brake Pedal goes to the floor when driving / sinking brake pedal

Master cylinder needs to be replaced.

If you are in Pakistan, suggest you buy a used original. The new ones are rubbish. Alternatively import one yourself

Fault 7 - Knocking sound when releasing brake pedal

The noise is coming from the brake booster. I tried lubricating the grommet behind the pedal, but with no success. Other than replacing the booster, if anyone can suggest another action, I am all ears.

Fault 8 - 4x4 wont engage or slow to engage / Diff lock wont engage or slow to engage

You need to change the central differential oil.

Slight tip: The FJ90 1kz is a full time 4x4. You must only engage the small gear if you are slipping or driving in very slippery conditions. If you drive the car with diff lock engaged for too long or in the wrong conditions, you risk destroying your rear axel. I strongly advise you get some training or do some research if you've never done it before.

Fault 9 - AC temperature not changing or heater not engaging

There can be a whole host of reasons for this fault. I have two cars in my family and in both this was our problem.

Inside the engine bay, behind the intercooler, attached to the car body is a valve. Attached to this valve is supposed to be a cable, goes from the valve to the motor located in the corner of passenger footwell.

When you turn the temperature on the climate control, you will hear the motor if you listen carefully.

In my case the cable was missing. This was also the case for the other car and it was a real pig trying to locate a replacement.

If you cant get the cable, you can turn the valve by hand as and when you need it.

Fault 10 - Accelerator pedal knocking while stationary

The Vacuum system is either not plumber correctly or there is a fault. I do have a guide, message me if you want to check the plumbing.

Fault 11 - Seat cushion uncomfortable

In my case I just got the existing seats re-foamed

Fault 12 - Mud Flaps going into the tyres

In my case there is a shortage in country for replacements. I simply tied the rear mud flaps back with a thin cable to the rear bumper

Fault 13 - Boot / tailgate wont shut

There is a fault with rear lock. You can replace it, or in my case I just placed some washers onto the hinge and it did the trick

Fault 14 - Fuel Gauge not working

Inside the fuel tank is a float valve which sends a signal to the dash and indicates the fuel level. In my case a very thin wire on the float had snapped and I managed to get away with having it soldered back on.

Fault 15 - Intercooler / Turbo not functioning correctly

Over the years the intercooler gets clogged with oil. You can have it cleaned and there are plenty of videos online on how to do it yourself

Fault 16 - Loud Hissing sound coming from Intercooler

In my case the pipe joint connecting the Intercooler to the air intake manifold had a huge crack. It seems this is a common problem. I could not find a replacement, so I filled the crack with heat resistant silicone tape and then wrapped the pipe with leather and for now it seems to plug the leak. I am still searching for a replacement part.
Yes, it started playing up, but there is something here locally the electrician did to get me a few more years
@JayZ ... It's funny that you mentioned. And it's good that you did. I've experienced all of these unfortunately
Good post , I'm sure its all mentioned on the forum somewhere but not in one place .

Fault 7 is a new one on me and i been using the forum maybe 10 years :think: air in the system would be my first thought ?
After changed booster brake 'not original'...knocking sound when release brake and accelerator pedal also knocking sometimes...i think fault 7 and 10 need to replace booster original to solve the problem
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