OBD-II trouble code
P2064: Reductant/Regeneration Supply Control Circuit High
This circuit has a chemically specific enemy that most circuits do not: the fluid it delivers. Urea solution that has crept along a wire corrodes copper and dries into a hard white crystal that lifts terminals apart — which is why the first move here is to look, not to measure.
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 P2064 mean?
P2064 means the module found the supply pump control circuit sitting higher than expected when it tried to drive it, or open when it expected a load. Electrically that is the standard high-side report, and it covers the usual population of broken wires, open windings and failed drivers. What makes this particular circuit different from every other circuit that can set a high code is where it lives and what surrounds it.
The supply pump's connector is on or immediately adjacent to the reductant tank header. Diesel exhaust fluid is an aqueous urea solution, and it gets onto that connector by three routes that have nothing to do with electrics: a weeping header seal, a spilled or overfilled tank, and the ordinary drips that come off a fill nozzle. Once a small amount has wicked into a connector, it behaves in a way road water does not. The water evaporates and the urea stays, and what it leaves behind is a hard, white, non-conductive crystal that grows in place. It grows between terminal faces and behind seals, and because it is a solid, it physically lifts contacts apart. The result is an open circuit created by a chemical deposit rather than by anything breaking.
That is the reason this code deserves a visual inspection before a meter. A greenish-white crust around a pin, a chalky ring on a connector face, or a pale streak running down a wire from the header is a diagnosis on sight, and it points straight at the repair. Measuring first works too, but it tends to end with a decision to replace a pump that is perfectly healthy and a connector that was the real fault.
There is a second, nastier property of urea in a harness, and it is the reason repeat failures on this code are common. Urea solution is aggressively corrosive to copper, and it does not stay at the connector. It wicks along the strands inside the insulation, following the wire away from the contamination point. What that produces is a wire that looks perfectly sound where you can see it, with green, powdery, high-resistance copper six or eight inches further back under intact insulation. A repair that re-terminates at the connector puts a new pin on a corroded conductor and fails again in months. The correct repair is to cut back until the strands are bright, which sometimes means replacing a longer section than the visible damage suggests.
The third consequence follows from the first two: the contamination has a source, and unless the source is fixed, the repair is temporary. If DEF is reaching the connector, something is letting it out — a header seal, a cracked fill neck, a loose line fitting, or a habit of overfilling. A repair on this code that does not end with an explanation of where the fluid came from is unfinished work, and the vehicle will be back.
Common causes
- Urea crystal deposits inside the tank header connector forcing terminals apart
- Copper corrosion wicking along the control wire from a DEF contamination point
- Weeping tank header seal or loose line fitting allowing fluid onto the harness
- Open in the supply pump control wire from chafe, rodent damage or a failed splice
- Supply pump winding open from wear or internal corrosion
- Control wire shorted to a battery or ignition supply, which also holds the circuit high
- Relay coil open or relay socket terminals no longer gripping
- Module driver output failed open
- Terminal backed out of the connector body after a previous tank or filter repair
- Blown fuse or open power feed leaving the circuit unable to pull down
Symptoms
- Check engine light on with the engine running normally
- White or pale crystalline residue visible around the tank, header or connector
- SCR or DEF message counting down to reduced power
- Supply pump silent when commanded
- Reductant level not falling despite many miles driven
- Cluster of reductant pressure and dosing codes stored at the same time
- Repeat failure of the same circuit a few months after a previous repair
- Damp patch or staining on the frame or underbody below the reductant tank
- Inducement warnings and staged power reduction as the countdown advances
- Fault present immediately after a tank, filter, heater or level sender service
Diagnostic steps
- 1.Look before you measure. Inspect the tank header, its connector and the first foot of harness for white crystalline residue, chalky rings on connector faces and pale streaks running down wires. Finding any of that is effectively the diagnosis.
- 2.Unplug the connector and inspect the terminal faces under good light. Deposits growing between contacts explain an open circuit with nothing broken.
- 3.If contamination is present, cut a wire back an inch at a time until the strands are bright copper. Green or powdery strands under intact insulation mean the corrosion has travelled and re-terminating at the connector will not last.
- 4.Find where the fluid came from. Check the header seal, the fill neck, line fittings and any evidence of overfilling. A repair that leaves the source in place fails again.
- 5.With the pump and module both disconnected, check the control wire for continuity end to end, and separately check it for voltage with the key on. Voltage present with no command means a short to a supply and should be repaired before the circuit is commanded again.
- 6.Measure the supply pump winding resistance. An infinite reading is an open load and accounts for a high reading without any wiring fault.
- 7.Check the fuse and relay for this circuit, and substitute a known-good relay of the correct part number rather than testing the original in place.
- 8.Ask what was serviced recently. The header connector is unplugged for filter, heater, pump and level sender work, and an unseated terminal after one of those jobs is a frequent cause.
- 9.Command the pump with a bidirectional tool and watch for current flow. No current with a command present confirms the open rather than inferring it from a voltage reading.
- 10.After repair, verify the pump runs and builds pressure, protect the repaired section with proper sealed splices and loom, and re-inspect the area after a few hundred miles to confirm no fluid is returning.
Repair cost
$130 – $1,800
Diagnosis is $120 to $250. Cleaning and re-terminating a contaminated connector is $150 to $450, and replacing a corroded section of the control wire adds to that in proportion to how far the corrosion travelled — budget $250 to $600 when a full section between the module and the tank has to be replaced. Fixing the contamination source matters: a header seal or line fitting is $60 to $350, while a cracked fill neck or tank can be $200 to $900. The supply pump itself is normally part of the tank header assembly, so a genuine pump failure runs $250 to $900 in parts with 1.5 to 4 hours of labour for draining and dropping the tank. A relay or fuse is $20 to $110 and is worth eliminating first. Module replacement with programming is $600 or more and is the uncommon outcome.
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.