OBD-II trouble code
P2046: Reductant Temperature Sensor Circuit Intermittent
A tank holding several gallons of fluid cannot change temperature quickly, so a DEF temperature reading that jumps is proving something about the wiring rather than about the fluid — which makes this one of the few faults you can convict before running a single test.
Quick facts
- System
- Powertrain
- Category
- Exhaust / Aftertreatment
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $90 – $1,200
- DIY difficulty
- Advanced DIY
Browse every code in P2000–P20E8, or start from the full code library.
What does P2046 mean?
Most intermittent codes are hard because the evidence is ambiguous: a signal that moves erratically could be a failing circuit, or it could be a sensor faithfully reporting something that really is erratic. P2046 is the rare case where that ambiguity does not exist, and the reason is thermal mass.
Diesel exhaust fluid sits in a sealed tank in quantities measured in gallons. Liquid in that quantity changes temperature the way a bathtub does — slowly, smoothly, and with a lag measured in tens of minutes. There is no driving condition, no ambient swing and no heater output capable of moving it several degrees between one sample and the next. So when the module sees a DEF temperature that steps, spikes, drops out or returns a default value and then comes back, it is not observing the fluid. It is observing its own circuit. That physical impossibility is what the code is built on, and it is why this fault does not need a second sensor to cross-check against the way a rationality code does.
The practical consequence is that the value itself stops being interesting and the rate of change becomes the whole diagnostic. A steady reading that happens to be wrong is a different fault with a different code. What matters here is a datalog captured at the highest sample rate the scan tool offers, because the signature you are hunting is a step where physics forbids one. Many tools will smooth or average a slow-moving parameter like fluid temperature by default, which is exactly the wrong setting for this code: the averaging will quietly hide the one feature you came to find. Turn it off, log raw, and drive the vehicle over surfaces that load the chassis.
The second thing worth understanding is where the electrical noise is likely to come from, because this circuit has an unusual neighbour. The tank heater — an electric element drawing meaningful current, switched on and off by the module — lives in the same header assembly as the temperature sensor, and on most designs their conductors leave through the same connector and run together in the same loom. That proximity is normally harmless, but it stops being harmless once a shared ground develops resistance or a shield or routing detail is disturbed during service. Heater current switching then couples into the sense lead, and the symptom is an intermittent that correlates with heater duty cycle rather than with road surface. That is a genuinely different fault from a broken wire, it points at grounds and routing rather than at the sensor, and the way to separate the two is to note whether the disturbance appears when the heater is commanded and disappears when it is not.
The third is that this code is a schedule, not an emergency. The module needs to see the fault arrive and then clear in order to classify it as intermittent, and a circuit that recovers is a circuit that has not finished failing. What that buys is a window in which the repair is a terminal, a pin tension, a ground stud or a length of loom rather than a tank assembly. It is worth using the window, because it closes on its own.
Common causes
- Terminal at the DEF header connector with reduced spring tension, losing contact under vibration
- Fretting corrosion on the signal or ground pin, breaking contact for milliseconds at a time
- Connector seal hardened or displaced, admitting moisture that bridges or interrupts depending on conditions
- A few broken strands inside an otherwise intact conductor in the tank harness
- High-resistance ground shared with the DEF tank heater, allowing heater switching to disturb the sense lead
- Harness routing disturbed during DEF pump, filter or level sender service, placing the loom against a moving or chafing surface
- Sensor element cracked by thermal cycling, producing a resistance that wanders
- Loom chafed where it crosses the tank strap or a chassis bracket, shorting only when the body flexes
- Corrosion inside the header connector from urea crystal creep along the conductors
- Reductant control module input stage fault or an unstable supply at the module
Symptoms
- Warning lamp that comes on, goes out by itself, and returns days later
- Scan tool DEF temperature that steps, spikes or drops to a default value and recovers
- Fault more likely on rough surfaces, over speed bumps or on washboard roads
- Disturbance that tracks the tank heater switching rather than the road
- Occasional refusal to dose after a start, followed by normal operation
- Companion DEF level or quality faults appearing sporadically from the same connector
- Intermittent DEF or SCR message on the dash with no consistent trigger
- Vehicle drives normally throughout
- Fault becoming more frequent over weeks or months
- Code eventually replaced by a steady circuit fault as the connection finally fails
Diagnostic steps
- 1.Log DEF temperature at the highest sample rate available and turn off any smoothing or averaging the scan tool applies by default. A slow parameter is usually filtered, and the filter will erase the step you are looking for.
- 2.Compare the logged trace against what a tank of liquid can physically do. Any change faster than a gradual drift is electrical by definition and removes the need to prove the sensor is wrong.
- 3.Note whether the disturbance coincides with tank heater commands. An intermittent that follows heater duty cycle points at a shared ground or routing problem, not at a broken conductor.
- 4.Open the DEF header connector and check individual pin retention by feel against a known-good terminal rather than by appearance. Relaxed tension does not look like anything.
- 5.Inspect pin faces for the dull grey powdery film of fretting corrosion, and check the connector seal for hardening, displacement or urea creep along the wires.
- 6.Measure voltage drop on the sensor ground path with the heater commanded on, since a return that is adequate at milliamps can be inadequate under heater current.
- 7.Wiggle-test in sections with the live value on screen: at the connector, along the tank crossing, at each bracket and where the loom transitions to the chassis.
- 8.Load the chassis rather than just the harness. Intermittents on underbody looms often need the body twisted, so drive it or use a lift that allows suspension articulation.
- 9.Check whether DEF level or quality faults are stored alongside. Several sporadic faults from one assembly indicate the connector rather than any single element.
- 10.After repair, clear the codes and re-log over the same road conditions that produced the fault, confirming the trace has gone smooth rather than simply that the lamp is out.
Repair cost
$90 – $1,200
Diagnosis is $120 to $250, and on this code it is the largest single variable because finding an intermittent takes road time. The outcome skews cheap: a retensioned or replaced terminal, a cleaned and re-torqued ground, or a section of loom repaired runs $100 to $400 and is the most common result. If the sensor itself has cracked, it is generally not sold as a separate part, so the job becomes a DEF header or heater and sender assembly at $250 to $900 in parts with 1 to 4 hours of labour. Catching the fault while it is still intermittent is what keeps this code in the lower band — once the connection fails permanently the diagnosis gets easier but the odds of a parts-level repair go up.
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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.