OBD-II Code
P1751
Severity
Not yet reviewed
Nobody on our side has assessed this code yet, so we are not going to guess at how serious it is.
Can you drive it
We cannot say
Treat it as unknown until a shop reads it with live data. If the check-engine light is FLASHING, stop driving as soon as it is safe to — that means an active misfire, whatever the code.
Indicative cost (USD)
$20–$450
From this code's diagnostic notes. Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
P1751 is a Mitsubishi-specific code meaning the TCM detected a fault in the A/T Control Relay (the relay that supplies switched battery voltage to all transmission solenoids and the TCM solenoid driver outputs) — either the relay isn't energizing when commanded, isn't dropping out when commanded, or the feed-voltage rail is out of spec.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then follow the diagnostic notes further down this page, in the order they are written.
They are written in the order a shop works this code, cheapest checks first. Where they name a component, inspect its wiring and connector before replacing it.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
Read the full diagnostic procedureP1751 is a Mitsubishi-specific code meaning the TCM detected a fault in the A/T Control Relay (the relay that supplies switched battery voltage to al…
P1751 is a Mitsubishi-specific code meaning the TCM detected a fault in the A/T Control Relay (the relay that supplies switched battery voltage to all transmission solenoids and the TCM solenoid driver outputs) — either the relay isn't energizing when commanded, isn't dropping out when commanded, or the feed-voltage rail is out of spec. The A/T Control Relay sits in the underhood fuse/relay block on most Mitsubishi applications and acts as the master power switch for the entire shift-control circuit; when it fails, the TCM loses the ability to actuate any solenoid and the trans defaults to limp-mode (typically locked in 3rd gear with no torque-converter lock).
Cheapest-first ladder
- Pull the A/T Control Relay from the fuse block and swap it with an identical relay (horn, fuel pump, etc.) — if the fault clears, the relay was bad ($0 diagnostic, $15 replacement).
- Verify switched-battery voltage at the trans connector on the solenoid feed pin with KOER — should be battery voltage (12.5-14.5V); if 0V with KOER, the relay isn't energizing or the relay-control wire from the TCM is open.
- Backprobe the TCM relay-control pin per FSM — should be 12V key-off (relay coil de-energized) and 0V key-on (TCM pulls the coil to ground to energize); no transition means TCM driver dead or open in the control wire.
- Check the trans-solenoid feed fuse — a blown fuse on the relay output side will set P1751 along with multiple solenoid codes simultaneously. Expensive-misdiagnosis caveat: don't replace the TCM for a P1751 without first verifying the relay coil isn't stuck or the relay socket isn't carbon-tracked from a prior overheat — Mitsubishi's relay sockets are known to char internally after a solenoid short event, and replacing the TCM without replacing the socket causes the new TCM to fail the same way within weeks.
Vehicle-specific patterns2002-2007 Mitsubishi Lancer 2.0L (4G94) throws P1751 from relay-socket corrosion in the underhood fuse block after water intrusion past the box seal…
- 2002-2007Mitsubishi Lancer 2.0L (4G94) throws P1751 from relay-socket corrosion in the underhood fuse block after water intrusion past the box seal — common on cars parked outdoors in northern climates.
- 2004-2012Mitsubishi Galant 2.4/3.8L sees P1751 paired with multiple solenoid codes when the A/T relay fuse blows from a downstream solenoid short; trace and fix the short before replacing the relay or the new relay blows on first key-on.
- 2006-2012Mitsubishi Eclipse 3.8L and 2004-2011 Endeavor 3.8L share the same fuse-block layout and the same relay-socket carbon-track pattern.
- 2007-2013Mitsubishi Outlander 2.4/3.0L throws P1751 from a different failure mode — on CVT-equipped variants the A/T relay also feeds the stepper-motor power, and a stepper short pulls the relay coil out of range.
- 2001-2006Mitsubishi Montero Sport 3.5/3.8L sees P1751 from harness corrosion at the firewall pass-through where the relay-output wire enters the cabin to reach the TCM.
Estimated repair$20 to $450.
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