P0073 on 2016-2020 Ram 3500: Ambient Air Temperature Sensor Causes and Fixes

What's Unique About the 2016-2020 Ram 3500

On these Ram trucks, the Ambient Air Temperature (AAT) sensor is located in the driver's side mirror, not in the front grille like on many other vehicles. Its signal is routed through the Driver Door Module (DDM), then to the Body Control Module (BCM), and finally the PCM. This unique wiring path means that a common point of failure is the wiring harness in the flexible boot between the driver's door and the truck's body, which can break from repeated opening and closing of the door. This can also cause other codes related to the driver's door controls to appear simultaneously, a fact noted in official TSBs.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Generation note: This range covers the end of the fourth generation (2016-2018) and the start of the fifth generation (2019-2020) Ram 3500. The AAT sensor is located in the driver's side mirror on both generations, but the specific wiring connectors and mirror designs differ. The fundamental cause—wiring damage in the door or a sensor issue—is the same across both generations. The issue is also common on Ram 1500 and 2500 models of the same era.

Symptoms You May Notice

• Check Engine Light is on.
• Incorrect outside temperature display, often showing a default low value like -40°F.
• Automatic climate control (A/C and heat) does not work properly or at all.
• Remote start features tied to temperature (like heated seats/wheel) may not activate correctly.
• Temperature reading on the display shows dashes "---" instead of a number.

Most Likely Causes

1. Damaged Wiring in Driver's Door Jamb 🔴 High Probability The AAT sensor wires run through the flexible boot between the driver's door and the body. Constant opening and closing of the door can cause these wires to fatigue and break over time. This is a widely documented failure point on Ram trucks.
   How to confirm: Peel back the rubber boot in the driver's door jamb and inspect the wires for visible breaks, chafing, or damage. The AAT signal wire is often designated as the (G31) circuit. Gently pull on individual wires to see if they stretch or separate. Test for continuity from the mirror connector to the body-side connector with a multimeter.
   Typical fix: Repair the broken wire(s) using butt connectors with heat-shrink tubing or by soldering in a new section of wire for a durable, weather-resistant fix.
   Est. part cost: $5-$15
2. Faulty Ambient Air Temperature (AAT) Sensor 🟡 Medium Probability → Shop Ambient Air Temperature Sensor The sensor is located in the driver's side mirror housing, where it can be susceptible to moisture, vibration, and damage, leading to internal failure.
   How to confirm: Disconnect the sensor and test its resistance with a multimeter. An open circuit (infinite resistance or 'OL') indicates a failed sensor. The resistance should be below 5.0 Ohms and should change if you warm the sensor with your hand. A known-good sensor has a resistance of approximately 9.45 kOhms at 79°F (26°C).
   Typical fix: Replace the AAT sensor. On most Ram mirrors, this sensor is accessible by removing a small panel on the underside of the mirror assembly. The Mopar OEM part number is often 68457701AA for this generation.
   Est. part cost: $15-$40
3. Aftermarket Mirror Installation 🟡 Medium Probability Many aftermarket tow mirrors, especially cheaper ones, do not include a built-in AAT sensor. Installing these mirrors without transferring the old sensor or adding a new one will immediately trigger a P0073 code.
   How to confirm: Check if the code appeared immediately after installing new mirrors. Verify if the aftermarket mirrors have a provision for the AAT sensor. Some owners report this code even with aftermarket mirrors that claim to have a sensor, indicating a poor quality sensor.
   Typical fix: Purchase and install a separate AAT sensor and harness designed for aftermarket mirrors, such as those from Boost Auto Parts (part #2843). Alternatively, transfer the original sensor from the factory mirror if possible.
   Est. part cost: $25-$50

Rare But Worth Checking

• Damaged Connector: The connector at the mirror or inside the door can become corroded or have bent/broken pins, causing an open circuit. One owner found bent pins on the sensor connector to be the root cause. Always inspect connectors when diagnosing.
• Faulty Driver Door Module (DDM) or Body Control Module (BCM): It is very rare for the control modules to fail, but possible. This should only be considered after all wiring and sensor issues have been ruled out. Other door-related codes would likely be present.
• Blown Fuse: In some cases, a fuse related to the sensor circuit could be blown. On 4th Gen Rams, this can be Fuse F99 (10A) in the main fuse box under the hood.

Diagnosis Steps

1. Read the fault codes with an OBD-II scanner to confirm P0073 is active.
2. Check the outside temperature reading on the dashboard. A reading of -40°F or another obviously incorrect value strongly suggests an AAT sensor circuit fault.
3. Visually inspect the wiring harness inside the rubber boot between the driver's door and the A-pillar. This is the most common point of failure. Peel the boot back from the connector on the body and check for broken wires.
4. If wiring looks intact, access the AAT sensor on the bottom of the driver's side mirror. Inspect the sensor and its connector for physical damage or corrosion.
5. Disconnect the sensor. Use a multimeter set to Ohms to measure the resistance across the sensor's two pins. An infinite reading ('OL') means the sensor is bad. The resistance should be under 5.0 Ohms.
6. If the sensor has resistance, test the wiring. Check for continuity on the signal wire (often designated G31) and return wire from the sensor connector back to the Driver Door Module (DDM) connector.
7. If continuity is good, check for voltage at the sensor connector with the key on. You should see approximately 5.0 volts. If not, check for a blown fuse (F99 on 4th Gen) before suspecting a module issue.
8. If the code appeared after installing aftermarket mirrors, the mirrors are the most likely cause. Either they lack the sensor or have a faulty one.

Parts You'll Likely Need

• Ambient Air Temperature Sensor (OEM #68457701AA) — This sensor fails internally or is required when installing aftermarket mirrors that lack one.
  Trusted brands: Mopar, Dorman, Standard Motor Products
  OEM price range: $11-$20
  Aftermarket price range: $15-$30
• AAT Sensor Wiring Pigtail/Harness — Needed to add a sensor to aftermarket mirrors or to repair a damaged connector. Boost Auto Parts makes a popular kit (part #2843) for this purpose.
  Trusted brands: Boost Auto Parts, Dorman
  OEM price range: $25-$40
  Aftermarket price range: $20-$35

Related Codes That Often Appear With This One

• U113D-00 — TSB #S2208000162 explicitly links P0073 with U113D-00 ('Lost Communication with Master Power Window Switch'). Since the AAT sensor and the window switch are both in the driver's door and their wiring passes through the same harness, a wiring break in the door jamb often affects both circuits simultaneously.
• P0072 — This code for 'Ambient Air Temperature Sensor Circuit Low' can appear if the wiring is shorting to ground instead of being open. Both codes point to a fault in the same circuit.
• P0070 — A more general code for 'Ambient Air Temperature Sensor Circuit Malfunction'. It is often seen alongside P0073, indicating a fault in the AAT sensor system.

Technical Service Bulletins (TSBs) & Recalls

• S2208000162: Links P0073 with U113D-00 (Lost Communication with Master Power Window Switch), strongly suggesting a wiring fault in the driver's door harness.
• S2208000080: Identifies P0073 as 'Ambient Air Temperature Sensor Circuit High'.
• 18-044-26: Lists P0073-00 'Ambient Air Temperature Sensor Circuit "A" High' as a potential code found during engine diagnostics.

Platform-Specific Known Issues

• TSB #S2208000162 notes that P0073 can appear with U113D-00, pointing to a wiring issue in the driver's door.
• TSB #S2208000080 and #18-044-26 also list P0073 as a known diagnostic trouble code related to the AAT sensor circuit being high or open.

Mechanic-Grade Diagnostic Values

• AAT Sensor Resistance — expected: Approximately 9.45 kOhms at 79°F (26°C), 2.488 kOhms at 131°F (55°C), and 336 kOhms at -40°F (-40°C).. Failure: An open circuit ('OL' on a multimeter) or a resistance value that does not change with temperature indicates a failed sensor.
• AAT Sensor Connector Voltage (Key On, Sensor Disconnected) — expected: Approximately 5.0 volts on the signal wire.. Failure: Voltage significantly above 5.2V could indicate a short to voltage. No voltage could indicate a broken wire or fuse issue.
• AAT Signal Circuit (G31) Resistance to DDM — expected: Below 5.0 Ohms.. Failure: Resistance above 5.0 Ohms indicates an open or high resistance in the (G31) AAT Signal circuit, likely a broken wire in the door jamb.

Scan Tool Commands That Help

• wiTECH: BCM Software Update/Reprogram — A Chrysler TSB for other models mentions a BCM software update to correct inaccurate or slow-to-update ambient temperature displays. While not directly for P0073, if the temperature reading is erratic but no hard circuit fault is found, checking for an available BCM update with a dealer-level tool like wiTECH could be a final diagnostic step.

Wiring & Ground Locations

• (G31) AAT Signal Circuit — This wire runs from the AAT sensor in the driver's mirror, through the flexible door jamb boot, to the Driver Door Module (DDM).. This is the primary signal wire. An open or short in this wire is the most common cause of P0073. A 'Circuit High' code specifically points to an open in this wire.
• (G931) Sensor Ground Circuit — This is the ground wire for the AAT sensor, which also runs through the door jamb boot to the DDM.. An open in the ground circuit can also cause a P0073 code, as it prevents the sensor from completing its circuit, leading to a high voltage reading at the PCM.
• 5th Gen (2019+) Mirror Connector Pins — On the main (white) mirror connector for 2019+ trucks, the AAT sensor wires are located at pins 1 and 6.. When installing an aftermarket sensor (like the Boost Auto Parts kit), the white wire goes to pin 1 and the black wire goes to pin 6. This is critical information for fixing P0073 after an aftermarket mirror installation.

Real Owner Repair Stories

• Boost Auto Parts (YouTube) (2019+ Ram 1500/2500/3500 (5th Gen)) — Check Engine Light with code P0073 immediately after installing aftermarket tow mirrors.
  ❌ Tried (didn't work) The aftermarket mirrors were installed, which lacked the factory AAT sensor, causing the code.
  ✅ What actually fixed it Installed a dedicated aftermarket AAT sensor harness (Boost Auto Parts P/N 2843). The harness wires were inserted into the empty slots (Pin 1 and Pin 6) of the main mirror connector, and the new sensor was plugged in. The CEL was then cleared with a scan tool.
• RamForum.com user (4th Gen Ram) — P0073 and P0070 codes, AAT reading -40F after using the factory block heater. The reading initially went very high (150+ F) before failing completely.
  ❌ Tried (didn't work) Replacing the AAT sensor twice., Disconnecting the battery.
  ✅ What actually fixed it The final resolution was not posted, but the discussion confirmed that -40F indicates a complete loss of signal (open circuit) and pointed the user toward checking the wiring harness for damage, as replacing the sensor did not fix the issue. This reinforces that the wiring is a more likely culprit than multiple bad sensors.

OEM Part Supersession History

• 68138681AB, 68138681AC, 68138681AD, 68138681AE → 68457701AA — Standard part revision and consolidation over model years.

Model Year Variations Within This Range

• 2019-2020 (5th Gen): The main mirror connector is white, and the AAT sensor pins are specifically Pin 1 and Pin 6. This is crucial for anyone adding a sensor to aftermarket mirrors on a 5th generation truck.
• 2016-2018 (4th Gen): While the cause is the same, the specific door module and mirror connector pinouts may differ from the 5th Gen. Fuse F99 in the underhood Power Distribution Center is often related to this circuit on 4th Gen trucks.