What does it mean?
OBD II fault code U1110 is a manufacturer specific code that is defined by carmaker Mitsubishi as, “A/C-ECU Timeout”, and is set when the PCM (Powertrain Control Module) detects a communication failure between the A/C control module and the ETACS ( E lectronic T otal A utomobile C ontrol S ystem)* control module.
In the context of this code, a “time-out” occurs when communication between the ETACS-ECU and A/C-ECU fails for three consecutive seconds or longer over the CAN (Controller Area Network) serial communications line while the battery voltage is higher than 10 volts. * Some sources Mitsubishi-related technical information translate ETACS as “Electronic Time and Alarm Control System”. NOTE: Note that code U1110 only applies to Mitsubishi products with automatic A/C or climate control.
While code U1110 can and does sometimes appear on Mitsubishi products without automatic A/C control, the presence of this code on such vehicles is a kind of “ghost” code, and therefore, the code does not indicate issues either in the A/C system or in any CAN (Controller Area Network) or other serial bus communication system.
In its simplest form, the ETACS-ECU on Mitsubishi products is not only an “all-in-one” replacement for large sections of wiring and multiple fuse boxes- but it is also designed to control all the electronics systems on a vehicle that used to be controlled by various separate control modules.
In addition, The ETACS-ECU also distributes power and controls up to 30 switches to establish communications to systems like the A/C, windshield wipers, taillights, headlights, brake lights, power door locks, and many others via up to four high-speed CAN (Controller Area Network) systems and the slower LIN communications system.
We need not delve any deeper into the complexities of the ETACS-ECU and its relationship to body control functions here, beyond saying that the development of ETACS technology has made it possible to control systems like the A/C without manual inputs, apart from the driver or passenger making an initial temperature setting.
However, for this system to work as intended, the CAN network that controls the A/C system has to be in perfect working order, meaning that communication between the A/C control module and the ETACS-ECU has to be consistent, reliable, and free of electronic noise or interference.
Therefore, when the ETACS-ECU loses communication with the A/C control module for longer than three consecutive seconds, the ETACS-ECU will recognize that it cannot control the A/C system effectively and it will set code U1110, and possibly illuminate a warning light as a result.
Symptoms
- Climate control display blank, frozen or not responding to buttons
- Blower speed or temperature not following the selected setting, or the system defaulting to one output
- Air conditioning cutting out intermittently and then returning
- A warning lamp or information message appears together with the stored code
- The code often shows up after a jump start, a flat battery or battery replacement
- Other body electronics behave oddly at the same time
Likely causes
- Loose, corroded or partly unplugged connector at the back of the climate control head
- Damaged serial data wiring between the climate control head and the body control unit, often behind the dash or in the instrument panel harness
- Weak battery, poor charging output or a bad main ground, which makes modules drop off the bus during cranking and at idle
- Internal failure of the climate control head
- Failure inside the body control unit that manages climate communication
- Water intrusion into the dash harness from a leaking windscreen seal or a blocked evaporator drain
- On vehicles without automatic climate control this code can appear as a stored ghost code with no real fault behind it
How to fix it
- Load test the battery and check charging voltage and main ground connections
- Establish whether the vehicle actually has automatic climate control; without it, this stored code is not evidence of a real fault
- Unplug and inspect the climate control head connector for pushed-back pins, corrosion and heat damage, then reseat it
- Check power and ground at the climate control head with the circuit under load
- Check continuity and shorts on the data lines between the climate control head and the body control unit
- Watch climate control live data with the scan tool while wiggling the dash harness to catch an intermittent dropout
- Replace the climate control head or the body control unit only after wiring, grounds and supply voltage are proven good