P20AE — Reductant Metering Unit Temperature Sensor Circuit Low
**Overview of the code**
The diagnostic trouble code **P20AE** indicates a problem related to the **temperature sensor circuit of the reductant metering unit**. In simple terms, this code suggests that the engine control unit (ECU)—the vehicle’s computer—detects an abnormal or « low » reading from the temperature sensor responsible for monitoring the reductant metering system.
**Note**: Labeling and code references may vary between vehicle manufacturers, and the exact nomenclature might differ slightly depending on the make and model.
**Fast Facts**
- System affected: SCR (Selective Catalytic Reduction) system, specifically the reductant (AdBlue/DEF) metering unit
- Severity: Moderate, typically linked to emissions and system functionality
- Main symptoms: Possible warning lights, reduced performance, or emissions-related issues
- Driveability: Limited — driving is possible, but resolution is recommended to prevent further complications
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Manufacturer variations for trouble code P20AE
Different vehicle manufacturers may assign different labels or code structures to the same diagnostic issue. The label P20AE is managed within the OBD-II standard, but specific OEMs might have their unique nomenclature or subcodes to further specify the issue.
Known variations include:
- Fiat/Chrysler: P20AE – “Reductant Metering Unit Temperature Sensor Circuit Low”
- Volkswagen/Audi: Specific subcodes relate to SCR system issues, but P20AE remains consistent with OBD-II listing
- Mercedes-Benz: Could appear with similar description but may involve manufacturer-specific subcodes or labels
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What does trouble code P20AE mean?
The code **P20AE** is set by the ECU when it detects that the **temperature sensor in the reductant metering unit** is reading values that are abnormally low or that the circuit is experiencing a **voltage or connectivity issue**.
The **reductant metering unit** is a component that controls the amount of DEF (Diesel Exhaust Fluid) injected into the exhaust system to help reduce emissions. The **temperature sensor** within this system helps monitor the temperature of the fluid or the metering unit to ensure safe and proper operation.
This code is typically triggered when the ECU senses that the **sensor’s signal falls outside expected parameters**—for example, if the sensor reports a temperature that is too low or if there is an issue with the sensor’s wiring or circuit.
**Typical context of appearance**: You might notice this code after a cold start, during vehicle emission testing, or while performing vehicle diagnostics related to SCR system faults.
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Severity and risks of trouble code P20AE
The **severity** of P20AE depends on whether the issue is purely electrical or if it has a direct impact on emissions and engine performance.
If the problem is not addressed, the vehicle may enter **limp mode** in certain cases, or the emissions system may not function correctly, leading to increased pollutants and potential failures in emissions tests.
**Risks include**:
– Increased exhaust emissions and potential failure of emissions testing
– Possible damage to SCR components if the temperature sensor circuit problem is caused by a wiring short or open circuit
– Reduced effectiveness of the DEF system, which may impair NOx reduction
**Conclusion**: This code generally indicates **a limited driving risk**, but addressing it promptly is advised to prevent further system complications or non-compliance with emission standards.
**Can the vehicle be driven?**
Limited — the vehicle usually remains drivable, but the issue should be corrected quickly to ensure proper operation.
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Symptoms of trouble code P20AE
Signs of this fault are often mild but may include some noticeable indicators:
– **Warning lights** such as the **check engine light** or specific emission control advisory lights illuminate on the dashboard
– **Reduced engine performance** or a temporary limp mode activation in some vehicles
– **Increased emissions or failed emissions test**
– Sometimes, no apparent symptoms, with the code detected via diagnostic scan tools
Common symptoms are generally related to the **emissions control system’s operation** rather than immediate driveability issues, but alerting to maintenance is crucial.
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Most likely causes of trouble code P20AE
Trouble code P20AE can stem from various issues, but **certain causes are more common**:
*This list is ordered from the most to the least probable causes.*
1. **Faulty or damaged temperature sensor in the reductant metering unit** – The sensor itself may be defective, providing incorrect or inconsistent readings.
2. **Wiring issues** – Broken, frayed, corroded, or poorly connected wiring or connectors between the sensor and the ECU.
3. **Electrical circuit problems** – Short circuits or open circuits in the sensor’s circuitry affecting the signal transmission.
4. **Contamination or build-up in the sensor or circuit** – Dirt, debris, or deposits may interfere with proper sensor function.
5. **Actual temperature issues within the reductant metering system** – Rare but possible, such as if the system is exposed to unusual temperature extremes.
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How to diagnose trouble code P20AE
Diagnosing P20AE involves a systematic approach to verify the source of the problem while ensuring safety and avoiding unnecessary disassembly.
*Keep in mind, some steps may require specific tools or knowledge about the vehicle’s SCR system.*
1. **Visual Inspection**: Check wiring, connectors, and sensor condition for obvious damage, corrosion, or disconnection.
2. **Scan Data Review**: Use a professional OBD-II scanner to view live sensor data and compare readings against expected parameters.
3. **Check for other related codes**: P20AE might be accompanied by codes indicating coolant or other sensor issues.
4. **Test sensor continuity**: Perform electrical tests on the sensor wiring harness to verify circuit integrity.
5. **Sensor resistance checks**: If accessible, measure the sensor’s resistance with a multimeter, following the manufacturer’s specifications.
6. **Inspect the reductant metering system**: Look for contamination, leaks, or blockages that could affect temperature or system operation.
7. **Test the circuit with a known-good sensor**: Replace temporarily if possible to validate whether the original sensor is faulty.
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Possible repairs for trouble code P20AE
Resolving P20AE typically involves addressing electrical, sensor, or wiring faults:
– **Replace the faulty temperature sensor** — a basic repair best performed by a professional or an experienced technician.
– **Repair or replace damaged wiring and connectors** — involves cleaning, re-soldering, or replacing wiring harness sections.
– **Ensure proper connector engagement and corrosion prevention** — regular inspection and maintenance of electrical connections.
– **Clean or service the reductant metering system** — removing dirt or deposits that may interfere with temperature readings.
– **Verify system grounding and power supply connections** — ensuring stable electrical contact.
**Note:** If the sensor or wiring appears intact, but the problem persists, further investigation by a professional using manufacturer-specific tools and procedures will be necessary.
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Vehicles commonly associated with trouble code P20AE in Europe
This code primarily appears in diesel vehicles equipped with SCR systems to meet stringent emissions standards, especially in the VW Group and Fiat Chrysler models.
**Common makes and models include:**
– **Volkswagen Group**: Volkswagen, Audi, Škoda, SEAT (with diesel engines fitted with SCR and DEF systems)
– **Fiat/Chrysler**: Jeep, Dodge, Ram, Fiat models with SCR systems
– **Mercedes-Benz**: Certain diesel models with SCR technology
– **Renault and Peugeot**: Some diesel vehicles configured with SCR systems
The specific engine families affected are usually those incorporating the latest emissions control technology, generally in Euro 6 compliant models.
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Frequent mistakes with trouble code P20AE
Incorrect diagnosis or repair can lead to unnecessary costs or overlooked issues. Common mistakes include:
– **Replacing parts without proper testing** — such as swapping sensors without verifying wiring integrity or live data.
– **Ignoring related system issues** — like electrical circuit damage or contamination, which can cause false sensor faults.
– **Overlooking the importance of proper grounding and wiring repairs** — passive fixes that neglect electrical integrity often recur.
– **Assuming the sensor is always at fault** — other causes like wiring or circuit problems might be the actual culprits.
– **Neglecting manufacturer-specific procedures** — especially in vehicles with complex SCR systems that demand specific diagnostic steps.
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FAQ — trouble code P20AE
**Can this code disappear on its own?**
In some cases, if the cause is temporary—like a loose connector or transient electrical issue—the code may clear after fixing the problem or after repeated driving. However, persistent issues usually require repairs to prevent reappearance.
**Can I keep driving?**
Yes, in most cases, the vehicle remains drivable with this code set. However, you may experience reduced emissions performance, and some vehicles could enter limp mode to protect the system. It’s recommended to schedule repairs promptly.
**Why does the code return after clearing?**
The cause—faulty wiring, contaminated sensor, or actual temperature issues—remains unresolved, leading to the code reappearing. Proper diagnosis and repair are necessary to fix the root cause and prevent recurrence.
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This comprehensive guide provides clear insights into troubleshooting and resolving code P20AE, ensuring the vehicle’s emissions system functions properly and maintaining compliance with environmental standards. Always refer to specific manufacturer repair manuals for detailed procedures and specifications.