U1110 – A/C-ECU Time-out (Mitsubishi)

By Reinier (Contact Me)
Last Updated 2021-12-09
Automobile Repair Shop Owner

Table of Contents

1. What Does Code U1110 Mean?
2. Where is the U1110 sensor located?
3. What are the common causes of code U1110?
4. What are the symptoms of code U1110?
5. Get Help with U1110

What Does Code U1110 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 (Electronic Total Automobile Control System)* 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.

Where is the U1110 sensor located?

This image shows the appearance of the ETACS-ECU on a Mitsubishi Lancer. Note that while the ETACS unit forms part of the main fuse box on this application, this unit can also be located elsewhere on other Mitsubishi products. Other locations could be under the dashboard, or inside center consoles, but note that as a general rule, ETACS-ECUs are not repairable- at least, not reliably.

What are the common causes of code U1110?

The most common causes of code U1110 are largely similar across applications, and could include one or more of the following-

• Damaged, burnt, shorted, corroded, or disconnected wiring and/or connectors in the CAN line between the A/C-ECU and the ETACS-ECU, or in the power supply to the A/C-ECU
• Failed or defective A/C-ECU
• Failed or defective ETACS-ECU
• Failed or failing PCM, but note that this is rare

NOTE: Be aware that all replacement ETACS-ECUs must be programmed with a software version that is compatible with the software version/ calibration of the PCM. In Mitsubishi-speak, this is known as “variant coding”, meaning that the variant coding file must be copied from the original ETACS-ECU before the ETACS-ECU is replaced.

What are the symptoms of code U1110?

Common symptoms of code U1110 could include one or more of the following-

• Stored trouble code and possibly an illuminated warning light
• One or more additional UXXXX (Communication) codes may be present along with U1110
• The A/C system might be unavailable
• The A/C system may work intermittently, or may not perform as expected

NOTE: Be aware that proper diagnosis of code U1110 requires the use of Mitsubishi-specific equipment and software, as well as access to relevant and current service/repair information. For instance, the use of an oscilloscope is required to verify the functionality of suspect/affected CAN lines, the positive and negative waveforms of which should mirror each other exactly.

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