OBD-II trouble code
P2063: Reductant/Regeneration Supply Control Circuit Low
The most common wrong answer on this code comes from the meter, not the vehicle. This pump is usually speed-controlled by a pulsed signal, and an ordinary voltmeter averages that pulse into a low reading — so a perfectly healthy circuit measures 'low' to anyone who does not know what they are looking at.
Quick facts
- System
- Powertrain
- Category
- Exhaust / Aftertreatment
- Severity
- High severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $130 – $1,800
- DIY difficulty
- Advanced DIY
Browse every code in P2000–P20E8, or start from the full code library.
What does P2063 mean?
P2063 is stored when the control module sees the voltage on the reductant or regeneration supply pump control circuit sitting below the range it expects. As with its siblings, the module is watching its own output rather than the fluid, so this is a report about electricity, not about how much reductant reached the exhaust.
The detail that matters most on this member, and the one that causes more misdiagnosis than any other, is how the pump is driven. A supply pump is not a simple on-off device on most modern systems. The module has a pressure target to hit and a pressure sensor telling it where it currently is, so it modulates the pump — switching the circuit on and off many times a second and varying the proportion of on-time to control speed. That is pulse-width modulation, and it has a specific and awkward consequence for anyone testing with a standard digital multimeter. A DVOM in DC volts reports an average. A circuit switching between battery voltage and ground at, say, thirty percent duty reads as roughly thirty percent of battery voltage on the display — a number that looks exactly like a fault and is in fact the system working correctly.
So the first rule on this code is to use an instrument that can see the waveform: an oscilloscope, or at minimum a meter with a duty-cycle or frequency function. What you are looking for is not a voltage but a shape — clean square edges, a duty cycle that changes when the commanded pressure changes, and a low state that actually reaches close to ground. A real circuit-low fault shows up as a waveform that cannot get back up to battery voltage on the off portion of the cycle, or as a flat line near zero where a modulated signal should be.
The second useful consequence of that closed-loop control is behavioural, and it is audible. Because the module is regulating to a pressure target, a circuit that is partially shorted or leaking current to ground makes the pump underperform, and the module responds by commanding more. The pump runs harder, for longer, and noticeably louder, often continuously rather than in the short bursts an owner is used to. That pattern — a supply pump that has become conspicuous — is a genuine field indicator that something on the low side is wrong, and it distinguishes this code from the open-circuit member, where the pump simply goes quiet.
Finally, there is a cost boundary on this circuit that is worth finding early because it separates two very different bills. The supply pump on most designs lives inside or on top of the tank header assembly, which means reaching it involves draining and frequently dropping the reductant tank. The wiring between the module and that assembly, by contrast, is accessible. Both a chafed frame-rail wire and a failing pump can produce this code, and from the driver's seat they are identical. The header connector is the boundary between them: test there first, and the result tells you which side of that cost boundary the fault lives on before any tank is touched.
Common causes
- Control wire shorted to ground along the frame rail run to the tank
- Chafed insulation where the reductant harness passes a bracket, heat shield or suspension component
- Water or salt intrusion in the tank header connector creating a partial path to ground
- Supply pump winding shorted internally, lowering circuit resistance
- Damaged or crushed loom section from road debris under the vehicle
- Corroded splice in an earlier harness repair breaking down under vibration
- Module driver partially shorted, holding the output low
- Pump mechanically loaded by a clogged reductant filter, raising current draw
- Incorrect or aftermarket pump with different electrical characteristics than the module expects
- Rodent damage to the tank harness, which is a common failure point on vehicles parked outdoors
Symptoms
- Check engine light on with no change in engine performance
- Supply pump running louder, longer or continuously instead of in short bursts
- SCR or DEF message with a distance or time countdown to power reduction
- Reductant pressure codes stored alongside this one
- Repeated blowing of the reductant system fuse
- Fault appearing or worsening in wet weather and clearing in dry weather
- Reductant consumption higher than expected with no visible leak
- Staged power reduction once inducement advances
- Code returns within a short drive after clearing rather than after a full cycle
- Warm or hot connector at the tank header after a period of driving
Diagnostic steps
- 1.Before concluding anything from a voltage reading, determine whether this circuit is pulse-width modulated on this vehicle. If it is, a plain DC voltmeter will report a low average on a perfectly healthy circuit and that reading means nothing.
- 2.Scope the control wire, or use a meter with duty-cycle mode, and watch the waveform while the module changes its commanded pressure. Clean edges with a varying duty cycle is a working circuit.
- 3.Listen to the pump during a normal drive cycle. A supply pump that has become continuous or noticeably louder is the module compensating for a circuit that cannot deliver, which supports a genuine low-side fault.
- 4.Test at the tank header connector first, because that connector is the boundary between an accessible wiring repair and a tank-out pump job. Results there tell you which side of the cost line the fault is on.
- 5.With the pump disconnected and the module disconnected, measure the control wire to ground. A low resistance confirms a short in the harness with both components removed from the equation.
- 6.Measure the pump winding resistance and compare with specification. A value materially below spec indicates shorted turns and a pump that must come out.
- 7.Inspect the header connector for moisture, salt and corrosion, and pull-test the individual terminals rather than judging by how the connector looks from outside.
- 8.Check the reductant filter service history. A clogged filter loads the pump, raises current and can drive the circuit outside its expected band without any wiring fault.
- 9.Raise the vehicle and walk the entire harness route to the tank, flexing at each securing point while watching a live reading, and look specifically for rodent damage and crush points.
- 10.After repair, clear the codes, verify the commanded and actual pressure track each other across a full dosing event, and confirm the pump returns to its normal intermittent operation.
Repair cost
$130 – $1,800
Diagnosis is $120 to $250 and is worth paying for on this code specifically, because the difference between the cheap outcome and the expensive one is a measurement most people take incorrectly. Repairing a shorted or chafed section of the tank harness is $150 to $550, at the top of that when the damage is mid-frame and the vehicle needs lift time. A reductant filter service, if a clogged filter is loading the pump, is $60 to $250. The supply pump is usually part of the tank header or delivery module rather than a separate part, so a pump failure lands at $250 to $900 in parts with 1.5 to 4 hours of labour for draining and dropping the tank. Module driver failure is uncommon and adds $600 or more with programming.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with def / scr reductant system service preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an advanced DIY job. It typically requires specialty tools, scan-tool access, lifting equipment, or careful sequencing to avoid causing new failures. Plan for extended downtime and have a backup vehicle. Most owners are better served by a shop that has done this repair before.