I have searched and read all the LS460 threads related to this issue and none of those threads fixed my issue. My cabin filter housing shroud isn't broken and the servo and its linkages to the shroud are all in perfect working order.

My ls460 recently started having the issue where there is a long boot time for the HVAC during cold starts and the HVAC will be in the off state and all settings return to default as well as the temperature to 75deg. I then manually turn it on and have to change all the settings to what I had before and the HVAC will function properly (blow cold, blow hot, various fan speeds, etc). All the air direction positions and their combinations (windshield, feet, face, etc) all function correctly. When I select each of the different positions, the air does get directed properly. So from a usage standpoint, the HVAC does work after this long boot time and resetting to default issue.

Techstream does pull the B1497 error code: BUS IC Communication Malfunction

I have already replaced the A/C Amplifier with a brand new part purchased from my local dealer and that did not solve the issue. The new amplifier was properly initialized using the techstream "servomotor initialization" function.



The only other thing the lexus service/repair manual states is to replace the A/C harness, which doesn't make sense: The A/C harness is just a bunch of wires and connectors, linking up all the various servos and sensors to the A/C amplifier, which is the ECU for the HVAC system. The harness itself doesn't have any ecu or circuitry in it. If there was a short, or cut wires in the harness, then one or more servos wouldn't respond or work. techstream didn't pull any servo-specific or sensor-related errors codes, just the B1497 code. As listed below, I have manually tested each servo function in techstream's live test section and found each servo working properly. I removed all the related trim to get visual access to each servo and watched them move their full range of motion when using the techstream live test feature.
:
Here's an image of an A/C harness I found online, it's just wiring and connectors:







Here's what I have troubleshooted and tested so far:

• I have examined and tested the cabin filter air inlet servo to make sure that it does open and close properly when the recirc button is hit. (the air inlet shroud and the servo does move, close, and open properly when the recirc button is hit)
• I have used techstream software to run live tests on all the HVAC-related servo and all of them functioned properly.
• Cabin air filter housing was replaced with a brand new genuine lexus part, as well as the filter element itself
• the filter housing does seat properly and securely in the blower motor housing.with no free play movement
• this issue occurs only after letting the car sit for a long period of time ( few hours, or overnight), if I turn on the car within 5 to 15 min, the hvac will retain settings and turn on almost immediately and automatically, like it should and has in the past
• There is no CEL and OBD II does not pick up any other error codes (pending or confirmed)

According to the service manual, a LOT of stuff needs to come out from the dash, including parts of the actual AC system. Has anyone actually replaced the AC harness and found an easier way to do it?

 

I remember another post in which the issue was pins being slightly pulled out of the plug that connects to the ac amp. The harness is tight in that area.

 

I double checked all pins in the connectors and all are good condition and fully in the connector head and not pulled out.

 

Your DTC chart is not what it is. Look for full FSM and recheck it's DTC chart for new info.

 

what’s the new etc chart? I only have one version of the repair manual.

 

Interesting read here...

https://www.clublexus.com/forums/rx-...-solution.html

 

I'm on vacation but somebody hopefully will chime in with updated B1497/97 DTC chart.
What I can see from here is list of reasons is extensive:

• Air conditioning harness
  
• Rear air conditioning harness*2
  
• Air conditioning amplifier
  
• Air mix servo motor (for driver side COOL)
  
• Air mix servo motor (for passenger side COOL)
  
• Air mix servo motor (for driver side HOT)
  
• Air mix servo motor (for passenger side HOT)
  
• Air mix servo motor (for driver side front A/C rear air flow)*1
  
• Air mix servo motor (for passenger side front A/C rear air flow)
  
• Air outlet servo motor (for driver side FACE)
  
• Air outlet servo motor (for passenger side FACE)
  
• Air outlet servo motor (for driver side FOOT/DEF)
  
• Air outlet servo motor (for passenger side FOOT/DEF)
  
• Air outlet servo motor (for driver side front A/C rear air flow)
  
• Air outlet servo motor (for passenger side front A/C rear air flow)*1
  
• Air inlet servo motor
  
• Cool air bypass servo motor (for driver side)
  
• Cool air bypass servo motor (for passenger side)
  
• Max hot bypass servo motor (for COOL)
  
• Max hot bypass servo motor (for HOT)
  
• Rear air outlet servo motor (for LH side)*2
  
• Rear air outlet servo motor (for RH side)*2
  
• Rear exhaust mode servo motor (for diffusion)*2
  
• Rear exhaust mode servo motor (for emission)*2
  
• Harness and connector
  

 

I have the full Dtc chart from the previous page in the service manual and it does shows all the servos having their own B codes in techstream . I assume if any of them or other components are faulty, it would throw the code specific to the faulty part. All servos did move their full range without issues when I tested it using tech stream active test function, so I thought it would rule out the servos.

 

You have a communication error, I would test bus wires to the AC controller. Communication lines are a little bit different than regular wires especially if it is a twisted pair which, I believe, is used in car communication networks. So you need to test not just continuity but resistance/voltage. If somebody messed with the wiring before, it will likely double work for you.

 

but if there were truly something wrong with the communicaitlines, wouldn’t the servos not respond to the active test in tech stream? The servos also reported the correct position number as well as I test each servo. That’s the weird thing: all manually active tests of each servo showed proper movement and reporting of position.

 

But the error states nothing about servos, it tells you that there is an issue with communication. It even tells you that there is a communication issue through the AC wire harness to the AC amplifier (between the ECU and the AC amplifier). I suspect, there is oxidation or physical damage to the comm link that causes intermittent connectivity.

The easiest thing to try is to disconnect all connectors (prior disconnect the battery) from the ECU and the AC amplifier, briefly inspect it and reconnect it back, reconnect the battery. If it does not help, check wires near connectors on both sides, look for any damage, misplacement etc. Do voltage check of the communication bus.

 

thanks for pointing this out. I will check the voltage later if I can figure a way to do it. But based on that’s post’s symptoms, I don’t think it’s the same problem (they do have a different code pulled; B1479 vs my B1497. My ac functions totally normal once I get it to turn on. The air blow cold when set to low temps and hot when set to higher temps. The air positions choices (face windshield feet) all function as intended when their respective buttons are pushed.

 

Dman Lexdysia

 

My 2012 LS AWD does the exact same thing! All I’ve done to fix the situation is replace the cabin air filter; no help. So rather than torment myself I’ve decided to live with it. HVAC system works perfectly except for this little glitch . But I can understand being driven stark raving mad by such a tiny thing: I’m that way too. Just not about this. Good luck!

 

https://priuschat.com/threads/b1497-....217637/page-2