OBD-II Diagnostic Trouble Code
P205B — Reductant Tank Temperature Sensor Range/Performance
P205B means the reductant tank temperature sensor reading is electrically in range but not believable. The ECM compares it to ambient and other temperatures after a cold soak, or expects it to change as the tank heats. The sensor is part of the DEF tank header unit on most trucks.
Severity 2/5
Truck-relevant
Service soon
Severity
Service soon
Reductant Tank Temperature Sensor Range/Performance
Code
P205B
Category
Powertrain
Subsystem
Aftertreatment
Truck-relevant
Yes
What this means for truckers
Service this week on a Cummins X15, Detroit DD15, PACCAR MX-13. Not an immediate stop, but ignoring it usually leads to a more expensive fix downstream.
Before you replace parts — try this first
P205B on the Aftertreatment system is most often drifted temperature sensor in the tank header — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
DEF warning and check-engine light, possible incorrect DEF heating in winter, limited dosing and an emissions derate countdown.
Common causes
- CommonDrifted temperature sensor in the tank header ($700–$2000)
- CommonHigh resistance from DEF corrosion at the connector ($100–$350)
- OccasionalFrozen DEF or failed tank heating so temperature does not change ($150–$2000)
- OccasionalA reference temperature sensor reading wrong ($100–$350)
How to fix
Compare tank, ambient and coolant temperatures after a cold soak
When to use: First step
Clean and check the header connector for voltage drop
When to use: When the reading is offset
Verify the tank coolant heating valve operates
When to use: When the code sets in cold weather
Replace the DEF tank header
When to use: When the sensor is confirmed bad
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → P2002 — Diesel Particulate Filter Efficiency Below Threshold (Bank 1)
- → P2003 — Diesel Particulate Filter Efficiency Below Threshold (Bank 2)
- → P2031 — Exhaust Gas Temperature Sensor Bank 1 Sensor 2
- → P2032 — Exhaust Gas Temperature Sensor Bank 1 Sensor 2 Low
- → P2033 — Exhaust Gas Temperature Sensor Bank 1 Sensor 2 High
Frequently Asked Questions
Can I drive with code P205B?
P205B is severity 2 — service this week. Not an immediate stop, but ignoring it usually compounds the problem. Most common cause for this code is a worn sensor or minor performance fault that won't strand you today but will get more expensive the longer you wait.
How much does it cost to fix P205B on a commercial truck?
Total repair cost ranges $100–$2000 depending on the root cause. The cheapest fix is usually the first one listed below — Drifted temperature sensor in the tank header — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P205B fail a DOT inspection?
Yes — P205B is an emissions-related code, and DOT inspectors check emissions compliance. An active emissions code with a check engine light can result in an out-of-service violation under FMCSA Part 393. The truck typically can't be moved until the code is cleared. Repeated emissions violations escalate to CSA scores.
What's the difference between P205B and related codes?
P205B is closely related to: P2002 (Diesel Particulate Filter Efficiency Below Threshold (Bank 1)), P2003 (Diesel Particulate Filter Efficiency Below Threshold (Bank 2)), P2031 (Exhaust Gas Temperature Sensor Bank 1 Sensor 2), P2032 (Exhaust Gas Temperature Sensor Bank 1 Sensor 2 Low). These codes share the same subsystem (aftertreatment) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P205B is set without the companions, the issue is more isolated.
How do I prevent P205B from coming back after a repair?
For P205B (Reductant Tank Temperature Sensor Range/Performance), prevention centers on the aftertreatment system. Run quality DEF (verify supplier — BlueDEF, PEAK, Yara Air1). Don't skip parked regens — when the dash asks for one, do it. Avoid extended idle time which fouls the DPF. Replace NOx sensors at the OEM interval (typically 400K miles).