Engine Undercovers
Lead Lap
Joined: Aug 2006
Posts: 4,759
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From: Texas
LOL. Man did I ever mess up this thread! The B2502 is an open in the RH Roof drive motor circuit. I disconnected plug S-20 to the Sliding Roof control ECU in the trunk area and read the continuity between pins 2 and 6. Good circuit reading would have been approximately 1 ohm. Mine read between 40 and 50 thousand or K ohms. Ordered a replacement motor from ebay for $59.98 and installed it yesterday afternoon. Repair complete. All top functions restored. But like I have said before, the helpfulness of the members of this forum is what makes it great. Thanks for caring.
Paul
Paul
Thread Starter
Racer
Joined: Aug 2019
Posts: 1,757
Likes: 355
From: CA
No Sir I didn't do the documentation because there is a very good exhaustive write up under a thread called "Roof Problem". Type in B2502 in the search bar and you will come up with three references. This thread is one, a thread I posted about why you should own a personal diagnostic tester and the "Roof problem" thread is the third. A treasure trove of very useful information is in that one for anyone needing to diagnose this kind of an issue. Thanks.
Paul
Paul
Pole Position
Joined: May 2016
Posts: 3,046
Likes: 626
From: AZ
I took it to mean the motors were turning at different speeds so the ECU made the top stopped working.
If I am right, then you may want to replace both motors, so they have the same wear and tear on them and you don't get this code.
BUT, THERE IS A GOOD CHANCE I AM WRONG, I just guessed at the meaning.
Thread Starter
Racer
Joined: Aug 2019
Posts: 1,757
Likes: 355
From: CA
OK. There are five wires to each of the motors. And they do indeed provide pulse modulation to count the revolutions of the motor. But unless the pulse detection circuit on the motor itself was defective, there should be no way that changing a single motor would have an adverse impact. But nice in-depth thinking. Thanks.
Paul
Paul
Pole Position
Joined: May 2016
Posts: 3,046
Likes: 626
From: AZ
OK. There are five wires to each of the motors. And they do indeed provide pulse modulation to count the revolutions of the motor. But unless the pulse detection circuit on the motor itself was defective, there should be no way that changing a single motor would have an adverse impact. But nice in-depth thinking. Thanks.
Paul
Paul
And, can you explain what Pulse Width Modulation is?
Does the Roof ECU Cause the modulation, or just count the modulation?
Sorry for all the questions, but now, you know why I was so excited that an electronics specialist joined the club lexus family.
Thread Starter
Racer
Joined: Aug 2019
Posts: 1,757
Likes: 355
From: CA
And they are excellent questions. This is of course a reasonable assumption because Lexus does not publish the interals of the electronic assemblies. And I dont own an Oscilloscope to be able to see the waveforms in action.
The ECU for the top has a chip inside that provides what is essentially a clock. It sends a square wave signal that switches at a specified frequency out to where it needs to go to be used for whatever. In this case, I believe that there is a special gear inside the motors gear assembly that uses a method called magnetic induction that produce the secondy signal that goes back to the ECU from each motor so that the ECU can keep track of each motors position. The signals the ECU is counting is on the smaller wires going to another sealed box on the motor while the two larger wires are carrying the higher current load needed to drive the motor itself.
I dont have a breakdown of all of the acronyms used in the schematics, but I believe that your assumptions about the third wire being a "return" (different from a ground) is basically correct. Voltage applied to one wire drives the motors in one direction, while voltage on a second wire drives it the opposite way. Hope that helps.
Paul
The ECU for the top has a chip inside that provides what is essentially a clock. It sends a square wave signal that switches at a specified frequency out to where it needs to go to be used for whatever. In this case, I believe that there is a special gear inside the motors gear assembly that uses a method called magnetic induction that produce the secondy signal that goes back to the ECU from each motor so that the ECU can keep track of each motors position. The signals the ECU is counting is on the smaller wires going to another sealed box on the motor while the two larger wires are carrying the higher current load needed to drive the motor itself.
I dont have a breakdown of all of the acronyms used in the schematics, but I believe that your assumptions about the third wire being a "return" (different from a ground) is basically correct. Voltage applied to one wire drives the motors in one direction, while voltage on a second wire drives it the opposite way. Hope that helps.
Paul
Last edited by Raven01750; Aug 21, 2019 at 01:54 PM.
Pole Position
Joined: May 2016
Posts: 3,046
Likes: 626
From: AZ
Interesting. So I can use a 7.5V battery pack to test the motor.
I understand how the 7.5 volts turn the motor, but I am confused on using terminals 4 & 5 to check voltage. Should the output voltage still be 7.5 volts? Or does the voltage read in pulses going from 0 to 7.5 off and on?
I understand how the 7.5 volts turn the motor, but I am confused on using terminals 4 & 5 to check voltage. Should the output voltage still be 7.5 volts? Or does the voltage read in pulses going from 0 to 7.5 off and on?
Thread Starter
Racer
Joined: Aug 2019
Posts: 1,757
Likes: 355
From: CA
Paul
Pole Position
Joined: Dec 2009
Posts: 3,135
Likes: 276
From: CA - San Diego
Kaise builds these for Denso and Toyota.
The multimeter and the current probe are strikingly similar to products of Kaise Corporation (pronounced kai-say), a Japanese maker of electrical instruments established in 1955. The multimeter appears to be a Kaise SK-6150(instructions), and the current probe appears to be a Kaise 660 (instructions). The versions produced for Toyota and DENSO (as the DGT-2) might have internal differences, but I think this is unlikely.
https://www.kaise.com/NewEnglish.htm.
The multimeter and the current probe are strikingly similar to products of Kaise Corporation (pronounced kai-say), a Japanese maker of electrical instruments established in 1955. The multimeter appears to be a Kaise SK-6150(instructions), and the current probe appears to be a Kaise 660 (instructions). The versions produced for Toyota and DENSO (as the DGT-2) might have internal differences, but I think this is unlikely.
https://www.kaise.com/NewEnglish.htm.
Thread Starter
Racer
Joined: Aug 2019
Posts: 1,757
Likes: 355
From: CA
LOL. You just had to do it didn't you. Listen. This thread was about Engine Under Covers and I do apologize for letting it get so off track. So lets wrap this up.
The last diagram Bob posted was on how to test a motor. That procedure should NEVER, EVER, EVER, EVER be tried while the motor is installed in your car.
If you do so I promise, severe and catastrophic destruction to your hinges.
The pulse modulation circuit from what I have been able to surmise does three things.
1. Synchronizes the motors on both sides of the car.
2. Tells the top when to stop by counting the revolutions of the motors.
3. Tells the motor to start in slow speed, switch to high speed and the back to slow speed so the top doesn't slam into the trunk or the front windshield pillors.
If that circuit fails, the top may still work but will ONLY work in slow speed. So, when someone says their roof only opens and closes really slowly, then they most likely have had a failure in this particular circuit which could be one of the motors OR the ECU itself.
Bob. You are a scholar and a gentleman. Thank you for all of the information you have provided for our "in the weeds" discussion today. 😉
Very sincerely
Paul
The last diagram Bob posted was on how to test a motor. That procedure should NEVER, EVER, EVER, EVER be tried while the motor is installed in your car.
If you do so I promise, severe and catastrophic destruction to your hinges.
The pulse modulation circuit from what I have been able to surmise does three things.
1. Synchronizes the motors on both sides of the car.
2. Tells the top when to stop by counting the revolutions of the motors.
3. Tells the motor to start in slow speed, switch to high speed and the back to slow speed so the top doesn't slam into the trunk or the front windshield pillors.
If that circuit fails, the top may still work but will ONLY work in slow speed. So, when someone says their roof only opens and closes really slowly, then they most likely have had a failure in this particular circuit which could be one of the motors OR the ECU itself.
Bob. You are a scholar and a gentleman. Thank you for all of the information you have provided for our "in the weeds" discussion today. 😉
Very sincerely
Paul