Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Upper Electronic Module (UEM)
Connector A, terminals #A1-#A22
The following values are measured between the relevant terminal in column 1 and terminal #A20 (signal ground) unless otherwise stated.
U = DC in volts (V).
Ubat = battery voltage in volts (V).
Ulow = voltage near 0 V.
| Terminal, breakout box | Terminal, control module | Signal type | Ignition off Active/not active |
Ignition on Active/not active |
Miscellaneous |
|---|---|---|---|---|---|
| #1 | #A1 | Power supply | Ubat | Ubat | - |
| #2 | #A2 | Third row reading lamps, control signal (XC90 only) | Ubat /0 V | Ubat /0 V | - |
| #3 | #A3 | Communication cable control modules (HS-CAN) | 2.5-3.5 V | 2.5-3.5 V | During communication. |
| #4 | #A4 | The front right reading lamp and general lighting, control signal | 7-9 V/0 V | 7-9 V/0 V | Active when the right front reading lamp or the general lighting is activated. |
| #5 | #A5 | Communication cable control modules (MS-CAN) | 1.5-2.5 V | 1.5-2.5 V | - |
| #6 | #A6 | The front right reading lamp, signal supply | Ubat /0 V | Ubat /0 V | Pulse width modulation (PWM) signal. |
| #7 | #A7 | Rear left reading lamp, signal supply | Ubat /0 V | Ubat /0 V | Active when the left rear reading lamp or the general lighting is activated. Pulse width modulation (PWM) signal. |
| #8 | #A8 | Extended X-supply | Ubat /0 V | Ubat /0 V | The power supply to the sun roof logic, mirror lamps in the sun visor, rain sensor, buttons for the headlining lighting and certain button lighting. |
| #9 | #A9 | Cargo compartment lighting (V70, V70 XC) / Third row reading lamps (XC90), power supply | Ubat /0 V | Ubat /0 V | Pulse width modulation (PWM) signal. |
| #10 | #A10 | Movement sensor (MMS) or movement sensor (IMS), power supply, (IMS replaces MMS for XC90 from and incl. model year 2012) | Ubat /0 V | Ubat /0 V | Supplies power to both MMS or movement sensor (IMS), (IMS replaces MMS for XC90 from and incl. model year 2012). |
| #11 | #A11 | Control module power supply | Ubat | Ubat | - |
| #12 | #A12 | Control module power supply | Ubat | Ubat | - |
| #13 | #A13 | Rain sensor, data signal | - | - | - |
| #14 | #A14 | Rear right reading lamp, signal supply | Ubat /0 V | Ubat /0 V | The signal is active when the button for the lamp is not pressed in. |
| #15 | #A15 | Rear left reading lamp, control signal | Ubat /0 V | Ubat /0 V | The signal is active when the button for the lamp is not pressed in. |
| #16 | #A16 | The front left reading lamp and general lighting, control signal | 7-9 V/0 V | 7-9 V/0 V | Active when the left front reading lamp or the general lighting is activated. |
| #17 | #A17 | The rear right reading lamp, signal supply | Ubat /0 V | Ubat /0 V | Active when the right rear reading lamp or the general lighting is activated. Pulse width modulation (PWM) signal. |
| #18 | #A18 | The front left reading lamp, signal supply | Ubat /0 V | Ubat /0 V | Pulse width modulation (PWM) signal. |
| #19 | #A19 | General lighting, signal supply | Ubat /0 V | Ubat /0 V | Pulse width modulation (PWM) signal. |
| #20 | #A20 | Signal ground | U~U=low | U~U=low | - |
| #21 | #A21 | Serial communication (Volcano lite) | 0 V-Ubat | 0 V-Ubat | The voltage is 0 V - Ubat during communication. Ubat is the default. |
| #22 | #A22 | Movement sensor (MMS) or movement sensor (IMS), (IMS replaces MMS for XC90 from and incl. model year 2012), data signal | Ubat | Ubat | Communication with both MMS or movement sensor (IMS) in XC90, (IMS replaces MMS in XC90 from and incl. model year 2012). |
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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