Evo VII–IX ACD/AYC Codes 45, 46, 81 and 82: What They Mean
By STANISLAV, FOUNDER, ACD/AYC PUMPS · UPDATED OCT 9, 2026
Codes 45 and 46 are the pressure sensor, 81 the pump relay, 82 no pressure. How to read them and what to check first.
If you own an Evo VII, VIII or IX, sooner or later the ACD mode lamp starts doing something strange — all the mode lights stay on after start, or the car stops locking the centre diff the way it used to. The ECU has stored a fault code. The four I get asked about most are 45, 46, 81 and 82, and they all point at the same corner of the system: the pump, its relay and its pressure sensor. Here's what each one means according to Mitsubishi's own workshop manual, and the order I'd check things in.
45, 46 (and 47) — the pressure sensor circuit. 81 — the pump relay circuit. 82 — the pump was told to run but pressure never came. Wiring faults first, pump last.
How do you read ACD/AYC codes on an Evo VII–IX?
You don't need a scan tool. The ACD and AYC share one control unit (the 4WD-ECU), and it can flash its codes through the ACD mode indicator on the dash:
- With the ignition off, earth terminal 1 of the 16-pin diagnostic connector under the dash (Mitsubishi uses a special harness; a jumper wire to earth does the same job).
- Turn the ignition on. Don't start the engine.
- Count the flashes of the ACD mode indicator. Long flashes (1.5 s) are tens, short flashes (0.5 s) are units, with a 2-second gap between the two digits and a 3-second pause between codes. So code 82 is eight long flashes, a pause, then two short ones.
- A steady rapid flicker (0.25 s) means no codes are stored.
With MUT-II or MUT-III you can read the same codes and also see live data — including the pressure sensor reading, which makes codes 45–47 and 82 much quicker to pin down.
Evo VII–IX ACD/AYC fault code table
This is the code list from the Evo VII workshop manual; the VIII and IX use the same numbers. The pump-related codes are highlighted — everything else is a sensor, switch or valve circuit. Codes 71–73 and 84 only exist on cars with AYC; a US-market VIII or IX has ACD only, so it will never show them.
| CODE | WHAT THE MANUAL SAYS |
|---|---|
| 12 | Valve power supply — open or short circuit |
| 13 | Fail-safe relay (inside the 4WD-ECU) — open or short circuit |
| 21–24 | Wheel speed sensor (FR, FL, RR, RL) — open or short circuit |
| 25 | Wrong tyre diameter |
| 26 | Wheel speed sensor — faulty signal |
| 31–34 | Steering wheel sensor — open, short or stuck output |
| 41 / 42 | Throttle position sensor — open circuit or ground / short circuit |
| 45 | Pressure sensor — open circuit or ground |
| 46 | Pressure sensor — open earth |
| 47 | Pressure sensor — abnormal power supply |
| 51 / 52 | Longitudinal G sensor — open or short / faulty sensor |
| 56 / 57 | Lateral G sensor — open or short / faulty sensor |
| 61 | Stop lamp switch — open circuit |
| 62 | ACD mode switch — stuck |
| 63 | Parking brake switch — short or not returning |
| 65 | ABS monitor — open circuit or ABS fault |
| 71 | AYC proportional valve — open or short circuit |
| 72 / 73 | AYC directional valve, right / left — open or short circuit |
| 74 | ACD proportional valve — open or short circuit |
| 81 | Electric pump relay — open or short circuit |
| 82 | Electric pump malfunction or pressure sensor defect |
| 84 | AYC control stopped (protection, not a fault) |
| 85 | ACD control stopped (protection, not a fault) |
Code 83 doesn't exist on the VII–IX. If you've seen it in a list online, that list is for the Evo IV–VI, which used a different AYC system with a pressure switch instead of a sensor.
What do codes 45, 46 and 47 mean?
All three are about the pressure sensor — the sensor that tells the ECU how much pressure the pump has built. They're electrical codes: the ECU is seeing a signal that can't be right.
- 45 — open circuit or ground. The sensor signal is below 0.2 V. Think broken signal or power wire, or a signal wire shorted to earth.
- 46 — open earth. The signal is above 2.0 V. Most often the sensor's earth wire is broken or the connector has lost contact.
- 47 — abnormal power supply. The 5-volt supply the ECU sends to the sensor is out of range.
Mitsubishi lists the same three causes for each: wiring or connector, the pressure sensor itself, or the ECU — in that order of likelihood. On a twenty-year-old car the connector is where I'd start: corrosion, a pin pushed back, a harness that's been chafing. Only when the wiring checks out does the sensor get replaced, and the ECU is a last resort.
One thing to understand: with a pressure sensor code the ECU can't see the pressure, so it shuts ACD and AYC down to be safe — even if the pump itself is perfectly healthy. Don't buy a pump for a 45 or 46.
What does code 81 mean?
Code 81 is the electric pump relay — the ECU has found an open or short in the relay's coil circuit. Causes: the relay, the wiring and connectors between the ECU and the relay, or (rarely) the ECU.
The quick check is to listen. The factory tool has an actuator test that runs the pump; without it, switch the ignition on and listen for the pump (at the back of the car, or at the front on US-market ACD-only cars). If it never runs, check the relay and its earth before anything else. A relay is a cheap part; a pump that has been running with a sticking relay often isn't — it overheats its own motor.
What does code 82 mean?
Code 82 is the one that worries owners, and it's the one most likely to mean real pump trouble. The manual's wording is “electric pump malfunction or pressure sensor defect”, and it's set when the ECU has commanded the pump to run, but the pressure sensor doesn't reach the specified value. It's the Evo VII–IX equivalent of C161E on the Evo X.
Mitsubishi lists six possible causes: low fluid, the pressure sensor, the pump relay, the hydraulic unit (the pump), wiring, and the ECU. Their diagnostic flow is a good one, and it's the order I'd follow too:
- Check the fluid level in the reservoir (in the boot on cars with AYC, at the front on US-market ACD-only cars), and look for leaks. Low fluid alone can set 82.
- Are 45, 46 or 47 stored as well? Fix the sensor circuit first — the 82 may just be a consequence.
- Is 81 stored as well? Fix the relay circuit first.
- Does the pump run? If it doesn't, check the relay's power feed (it comes from a fusible link) and its earth.
- If the pump runs but 82 keeps coming back, the manual's answer is to replace the hydraulic unit.
For reference, a healthy pump builds 1.0–1.6 MPa (about 145–230 psi) in the factory pressure test. In practice, on a high-mileage car with 82 and no other codes, the hydraulic side is usually worn — corrosion and wear inside mean the pump runs but can't build pressure fast enough. That's repairable: a proper rebuild restores the hydraulic section rather than just the motor.
What about codes 84 and 85?
These aren't faults. The ECU sets 84 (AYC) or 85 (ACD) when it switches the system off to protect it during very hard driving — think repeated launches or long stints of heavy wheelspin. Turn the ignition off and on again and control comes back. If they appear during normal driving, look for something else making the system work too hard, such as mismatched tyres (which can also set code 25).
How do you clear the codes?
With MUT-II/III, erase them from the ACD/AYC menu. Without a tool: ignition off, disconnect the battery negative for at least 10 seconds, reconnect, then let the warmed-up engine idle for about 15 minutes. If the fault is still there, the code will come back — clearing it only tells you whether the problem is current.
Parts for this job
Pick your car — each link goes straight to the part:
Not sure what your codes add up to? Send me the codes and what the car is doing, and I'll tell you where I'd look first. If the pump itself is worn, we restore it and load-test it before it ships — and you can trade in your old core.
