1992 LS400 - Check engine code 35 and transmission OD codes

threepwood · October 31, 2023

Check engine intermittently comes on and goes out. Code came up as 35, intermittent short in HAC. What in the world is HAC? Also, although it never came up while driving, the OD light was flashing at the same time as the engine code. It's either code 36 or 63, I can't tell. Symptoms are a terrible stumble when accelerating from 40 to 50 with a hot (normal temp) engine. Cold everything is fine. Any clue to decode these would be greatly appreciated. Thanks.

paulo57509 · November 2, 2023

Code 71 is EGR System Malfunction.

You're going to have to consult the Lexus service manual for details on how to diagnose what part of the system is at fault.

threepwood · November 3, 2023

Many thanks for your reply. But I have to point out that I don't have a code 71? However, your comment about a possible faulty EGR valve is really a great thought that had not occurred to me. I will plug it and see what happens, it could very possibly be the cause of the stumble between 40 and 50 mph.

I wouid also mention that my research elsewhere tells me that HAC may be some kind of High Altitude Compensation feed back to the ECU computer. Although I have not been able to find where this sensor is located, as it is not mentioned in the Lexus repair manuals.

paulo57509 · November 3, 2023

I could have sworn your post read, "Code 71".

Code 35: HAC = High Altitude Compensation

I would guess this is air/fuel mixture related; more effect of barometric air pressure than fuel. Thin air = richer mixture than at sea level. Back in the days of non-ECU controlled carburetors, driving at high altitudes would result in richer than normal air/fuel mixtures. We're talking thousands of feet....not hundreds. Highest point in FL is ~300 ft?

Code 36: There is no Code 36

Code 63: Open or short circuit in no. 2 solenoid valve (transmission). IRRC, this solenoid turns on to affect the 1-2 and stays on for the 2-3 shift in D range. Turns off to affect the 3-4 shift in D range.

The stumble you're getting may be the transmission not down shifting?