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I'm repairing Toyota Harrier ACU# (Automatic transmission) with no reversing problem. When gear is shifted to R she throws codes P0717 (input speed sensor A no signal) and P0793 (Intermediate shaft speed sensor no signal) and she does not enter in reverse gear. Oddly enough when reading live data (used both Toyota techstream software and Autoboss V-30) I see vehicle speed is 255 km/h but the vehicle is stationary

WHAT I HAVE TRIED SO FAR

1)I changed the Complete Automatic transmission and made sure AT fluid is on required level but no luck

2)I checked input shaft speed sensor and intermediate speed sensor but they are all okay, even tried to replace them but problem persists

3)Then I thought maybe ECU is faulty coz of the odd vehicle speed value I was getting and decided to replace the ECU but no luck

4)Inspected solenoids but they are all okay.

Currently I'm thinking may be due to ECU recognizing vehicle speed of 255 km/h(though vehicle is actually stationary) it forbids AT to shift Gears(shifting gears at that speed is dangerous and may kill the AT). But my assumption leaves me with un-answered qns like WHERE DOES THAT VEHICLE SPEED OF 255 KM/H COME FROM WHILE VEHICLE IS STATIONARY?

I tried disconnecting ABS ECU and the Wheel speed sensors But the vehicle speed still reads 255km/h on DATALIST

If ECU was faulty then why even after replacing the ECU I still got Vehicle speed of 255km/h

Those are just my ideas, can you guys help me how to fix this issue please

  • Have you checked for continuity between the speed sensors and the ECU? – HandyHowie Nov 13 '20 at 9:15
  • Or checked for a short on the wiring? – Solar Mike Nov 13 '20 at 9:22
  • The value 255 is suspiciously the maximum value that a computer byte can hold. Too many pulses coming through? – Weather Vane Nov 13 '20 at 11:22
  • @HandyHowie According to Toyota Harrier ACU# wiring diagram I see speed sensors are directly connected to the ABS and not to the ECU. On ABS side things are okay but on main ECU is where the problem starts – PeterNdomano Nov 13 '20 at 16:28
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You are getting the 255 because of the system not having any continuity to the sensors. It's the fall back for the system when there's no connectivity from the ECU to the sensors. My suggestion to you is you don't have the wiring connector to the transmission hooked up, or you've bent a pin when reinstalling the connector. In either case, check your work, then check to ensure something isn't damaged. Your wheel speed sensor shouldn't have anything to do with this, as it is primarily for the ABS. Also, remember, when working on vehicles, check what you've worked on ... other parts of the vehicle which you haven't have a VERY slim chance of causing you an issue (ie: things don't usually fail while sitting still ... they can, but it's highly unlikely).

  • I think there's continuity to the sensors coz I tried reading values while driving and the values are changing on AutoBoss Datastream but they are not the same as on the dash. For example when dashboard says vehicle speed is 30km/h my ECU datalist says it is 142km/h. I tried reading datastream using different devices and softwares but the results are the same – PeterNdomano Nov 13 '20 at 16:33
  • @Ndomano - What you are stating is in opposition to what your question states. Please ensure you give full and accurate information to get a full and accurate answer. – Pᴀᴜʟsᴛᴇʀ2 Nov 13 '20 at 16:37
  • @PAULSTER2 Nothing is in opposition sir, on the above explanations I stated the speed read when vehicle is stationary, here I was explaining what happens when we do a road test. In parking mode vehicle speed should be 0 but on data stream it's 255km/h when driven, vehicle speed read from data stream is almost 100+ km/h compared to the real speed on the dashboard's speedometer – PeterNdomano Nov 13 '20 at 18:30

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