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The mkiv Supra Owners Club

HAC Sensor Circuit


Markie

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Has anyone got experience with these? What do they do and where are they located?

 

Suddenly getting shutter and misfire tonight on way home.. Reset fuses etc and the error code I had when getting home was 35. Used the VVTi E1 TC wire trick to get the code..

 

Any ideas please?

 

I thought it could of been the Wynns injector cleaner I used the other day in the fuel, so filled tank hoping if it was that it would dilute it.. It's been working for days since adding it to the tank though.

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Not familiar with an HAC Sensor, can you elaborate?

 

After a little googeling its seems its an altitude compensation sensor with little effect and so far as I can see only fitted to the 7mgte during 88-89 don't think it was ever fitted to the 2jzgte from what I can see, unless it was only the US models.

Edited by Tricky-Ricky (see edit history)
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Just been doing some reading.. From what I gather the HAC/Barometric sensor is in the ECU.

Flow charts asks if there are any other codes, if answer yes continue, if answer no, replace ECU or ECM as they refer to it off the PDF I was reading.

 

Any ball park figure for a 98 VVT-i second hand one?

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From what I have just read from the manual, the HAC circuit is linked to the turbo pressure sensor (MAP sensor), and you need to check both the harness and the turbo pressure sensor, see page EG370, which its more likely to be, as if its the HAC then you will have to replace the ECU as its part of it, is the engine in limp mode? IE you cant rev more than 2,500RPM.

Edited by Tricky-Ricky (see edit history)
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Rightio.. Done some stuff.

 

o Opened up ECU. No sign of scorching or burn. No smell either. Refitted. Still the same.

o Cleaned Air Cone and Air Sensor. Refitted. Still the same.

o Disconnected battery

 

- It does not enter limp mode, no engine light or warning light either.

- Idles fine

- Seems to be ok lowish revs aswell, but then start cranking it up a bit and you get mis-fire/stutter.

 

I feels like when I needed to change the O2 sensor and you can fele it mis/stutter. This though is a much more violet noticeable affair.

 

I get the feeling its not the ECU, but after clearing the codes I still get the same one greeting me when getting home (Error 35)

 

Error 35 (Turbo Pressure sensor circuit) is what I found now, no idea where I got HAC from, seems there are a few screen shots for the Supra where the same codes mean slightly different things..

 

Anyone know what I can check for this error? Could it just be a Turbo sensor gone wrong. Where about is it in the bay? Got the feeling there are more than two?

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Is the Turbo pressure sensor the one above the turbos and where the air intake pipe comes into the top before it goes into the turbos..?

 

Is there only one as well?

 

The sensor is bolted to the inside face of the plenum near the back of it, it has one reference 6mm tube and a electrical connection plug.

 

Here,

image

Edited by Tricky-Ricky (see edit history)
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Spoke to Toyota who are after £260 for this little sensor. Does anyone have one spare I can borrow or buy?

If it was like £30-40 I would just get and try, but its a tad expensive if it is actually not the issue.

 

Was thinking of getting Toyota to do a diagnosis to double check, but not sure how much that is... :(

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  • 2 weeks later...

Update.. Had a Turbo pressure sensor from Brad. Try it this morning, still the same..

 

I have not reset the ECU yet, but I don't think it's gonna matter. But I will and see if I still get the Error Code 35

 

What I did do though from reading another Supra forum is test the voltage to the sensor which is meant to be about 4-5v and mine is showing 4.8-5 so does this mean the wires and ECU are fine?

 

It is starting to look like a Toyota diag now :(

 

Don't know if it's me, but the engine temp does not seem to reach it's usual temp, it seems to run a bit cooler going off the gauge.

Car still idles fine and seems ok at normal running. When Turbos seem to get more involved though it does start playing up again.

 

Would O2 sensor gone cause it? I did not think so as it was an instant problem from all fine and we'll and the next second, problems and very noticeable problems. Not like a more subtle misfire/splutter I have had before when O2 sensor needed changing,

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Just read a bit more.. If it's a FCD problem, would the ECU still log the fault or would ECU see all is well as the FCD is just an add on?

I use a HKS FCD.

 

What I think I am trying to say is that does the signal from the Turbo Pressure Sensor go back to the ECU via the FCD?

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Done some voltage checks today.. Seems like the sensor is feeding back voltage correct.

 

With ignition on I had 2.4v

Idle about 3.4v

 

Disconnected FCD just in case it was that but still the same problem and error 35.

 

Anyone got anymore idea or is it possibly ECU ?

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No it wouldn't but I was curious to see if thing improved, you say the onset of the problem was sudden, had you done/changed anything before it happened?

 

The fact that the error code give two possibles and that the MAP sensor has not improved things, then the next logical step would be to try and sap out the ECU for a know good one and see what happens.

Edited by Tricky-Ricky (see edit history)
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It's rare these sensors go. I would be more inclined to inspect the wiring to the sensor and the connector pins. There are only 3 wires, 5v, signal and ground. Old cars are now showing loom issues. I had to rebuild a TT auto loom not so long ago as it had the same issues as you with misfires over 10 psi.

 

There is bound to be someone on here can sell you one for around £20 notes.

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