P2045 — Reductant Temperature Sensor Circuit High #

Note: The wording of this code may vary by manufacturer. Below are some known variations:

• Reductant Temperature Sensor Circuit High Input (General, SAE)
• Diesel Exhaust Fluid (DEF) Temperature Sensor Circuit High (Ford)
• AUS32 Temperature Sensor Circuit High Input (Mercedes-Benz)
• SCR Urea Temperature Sensor Circuit High Input (GM, Isuzu)

Summary of the P2045 Code #

The P2045 diagnostic trouble code (DTC) signals that the Engine Control Module (ECM) has detected an abnormally high voltage in the circuit for the reductant temperature sensor. This sensor monitors the temperature of the reductant—commonly known as Diesel Exhaust Fluid (DEF) or urea—in vehicles equipped with Selective Catalytic Reduction (SCR) systems. The ECM relies on accurate temperature readings to properly dose and atomize DEF, which helps reduce nitrogen oxide (NOx) emissions. When the circuit’s voltage is abnormally high, the ECM cannot trust the sensor reading, which can compromise emission control. This code is often associated with diesel-powered vehicles using advanced emissions systems, particularly those manufactured after 2010.

Common Symptoms for Code P2045 #

When the P2045 code appears, you may notice symptoms ranging from subtle to severe. In some cases, the only sign is an illuminated Malfunction Indicator Lamp (MIL) or “Check Engine” light. If the DEF system is impaired, engine performance or emission levels may be affected. Here are the most frequent symptoms:

• Check Engine Light (MIL) illuminated
• DEF warning light or message displayed
• SCR or emission system warning light
• Possible reduction in engine power (limp mode)
• Increased DEF consumption or system faults
• Emission test failure
• No noticeable symptoms in some cases

Most Likely Causes for Code P2045 #

The P2045 code is most often triggered by issues in the electrical circuit or the sensor itself. Environmental factors, such as road debris or moisture intrusion, can also play a part. Below are the most common causes, listed from most to least frequent:

1. Faulty reductant (DEF) temperature sensor
2. Open or shorted wiring in the sensor circuit
3. Poor electrical connection at the sensor or ECM
4. Connector corrosion or damage
5. Failed power supply or ground circuit
6. Defective Engine Control Module (ECM) (rare)

Step-by-Step Diagnostic Guide for P2045 #

Diagnosing P2045 requires attention to detail and a systematic approach. Always begin with the basics before moving on to more complex checks. Follow these steps to pinpoint the cause:

• Use a scan tool to confirm the presence of P2045 and check for related codes (e.g., P2046, P20E2).
• Inspect the DEF temperature sensor and its wiring for obvious signs of damage, corrosion, or disconnection.
• Check the sensor connector for loose pins, corrosion, or moisture intrusion.
• With the ignition off, disconnect the sensor and measure resistance across the sensor terminals using a digital multimeter. Compare the value to OEM specifications.
• Check for reference voltage and ground at the sensor connector with the ignition on. Typical reference voltage is 5V, but confirm with OEM data.
• If wiring and sensor appear intact, use a jumper wire to simulate sensor input and watch for reaction on the scan tool.
• Test circuit continuity from the sensor connector to the ECM using a wiring diagram for your vehicle.
• If all wiring and the sensor check out, consider ECM diagnosis or reprogramming as a last resort.

Potential Repairs for P2045 #

Repairs should always address the root cause. Many fixes are straightforward, but thorough inspection is key to long-term reliability. Here are common repair actions:

• Replace the faulty DEF/reductant temperature sensor
• Repair or replace damaged wiring or connectors
• Clean corroded electrical terminals and apply dielectric grease
• Restore power or ground connections as needed
• Replace the Engine Control Module (ECM) (rare, after exhausting all other options)

Is it Safe to Drive with Code P2045? #

Limited — While you can usually drive with a P2045 code present, it is not recommended for extended periods. If the DEF system cannot operate correctly, your vehicle may enter a reduced power mode (“limp mode”) or fail an emissions inspection. In some cases, ignoring the code can lead to more severe DEF system malfunctions, potentially resulting in a no-start condition after multiple drive cycles. Addressing the issue promptly is the best way to avoid inconvenience or costly repairs.

Vehicles Most Commonly Affected by P2045 #

This code most often appears in diesel-powered vehicles equipped with Selective Catalytic Reduction (SCR) systems. It is especially common among:

• Ford Super Duty trucks (F-250, F-350, F-450 with Power Stroke engines)
• GM/Chevrolet Silverado and Sierra HD (Duramax engines)
• Ram 2500/3500 (Cummins diesel engines)
• Mercedes-Benz Sprinter (BlueTEC engines)
• Isuzu NPR and N-Series trucks
• Volkswagen and Audi TDI models (with SCR)

Common Mistakes & Best Practices for P2045 #

Misdiagnosis is possible with P2045, especially if the basics are overlooked. Here are common errors to avoid, and tips for a successful repair:

• Replacing the sensor without checking wiring or connectors
• Ignoring OEM wiring diagrams and pinouts
• Overlooking corrosion or moisture at connectors
• Forgetting to clear codes and verify repair with a test drive
• Not checking for software updates or recalls related to the DEF system

Quick FAQ for P2045 #

Q: Can a faulty DEF temperature sensor damage my engine?
A: No, the sensor itself won’t directly harm your engine, but it can trigger limp mode or cause your DEF system to misbehave, impacting drivability and emissions compliance.

Q: How much does it cost to fix P2045?
A: Costs vary by vehicle and labor rates. A new DEF temperature sensor typically ranges from $40 to $150, but wiring or connector repairs can add to the cost. Professional diagnosis and repair may run $150–$400, depending on complexity.

Q: Is it safe to clear the code and keep driving?
A: Clearing the code without fixing the underlying issue may cause it to return quickly. If your vehicle enters limp mode or DEF warnings persist, address the root cause promptly to avoid further issues.