P0098

What Does Code P0098 Mean?

DTC P0098 signifies an issue with the electrical circuit for Intake Air Temperature (IAT) Sensor 2, specifically indicating a “Circuit High” condition. The Engine Control Module (ECM) or Powertrain Control Module (PCM) monitors the voltage signal from IAT Sensor 2 to determine the temperature of the air entering a specific point in the intake tract. IAT sensors are typically Negative Temperature Coefficient (NTC) thermistors, meaning their electrical resistance decreases as the temperature of the air flowing over them increases, and vice versa. This resistance change directly affects the voltage signal returned to the ECM/PCM.

A “Circuit High” condition for P0098 means the ECM/PCM is detecting an abnormally high voltage signal on the IAT Sensor 2 input circuit, often approaching or at the 5-volt reference voltage. This high voltage typically occurs when the thermistor exhibits excessively high resistance, or an open circuit, preventing the voltage from dropping through the sensor. The ECM/PCM interprets this high voltage as an extremely low air temperature (e.g., -40°F or -40°C), well outside the expected operating range. This erroneous temperature input can lead to incorrect calculations of air density, subsequently impacting fuel trim, ignition timing, and potentially boost pressure control in forced induction systems. The “2” designation indicates this is a secondary IAT sensor, often found downstream of a turbocharger, supercharger, or intercooler, or in vehicles with multiple intake plenums, providing more granular temperature data for combustion optimization.

Common Symptoms

• Malfunction Indicator Lamp (MIL) Illumination: The “Check Engine” light will be illuminated on the dashboard.
• Reduced Fuel Economy: The ECM/PCM may enrich the fuel mixture due to an incorrect cold air temperature reading, leading to excessive fuel consumption.
• Poor Engine Performance: Symptoms such as hesitation, stumbling, rough idle, or a general lack of power, especially under acceleration, can occur.
• Incorrect Idle Speed: The engine may idle erratically or at an inappropriate RPM due to miscalculated air density.
• Failed Emissions Test: Elevated emissions of hydrocarbons (HC) and carbon monoxide (CO) due to an overly rich fuel mixture can cause a failure.
• Rough Idling or Stalling: While less common for a “circuit high,” severe miscalculation of air density can destabilize engine operation.

What Causes the Code P0098?

• Faulty Intake Air Temperature Sensor 2: The most common cause is an internal failure of the thermistor within the sensor, resulting in an open circuit or excessively high resistance.
• Wiring Harness Issues:
  • An open circuit (break) in the signal wire between the IAT Sensor 2 and the ECM/PCM.
  • An open circuit in the ground wire supplying the IAT Sensor 2.
  • A short to voltage within the signal wire, supplying 12V or other unregulated voltage to the ECM/PCM’s 5V reference input.
  • Corrosion or damage to the sensor connector or terminals, leading to an intermittent or open connection.
• Poor Electrical Connection: Loose or corroded pins at the sensor connector or the ECM/PCM connector can interrupt the circuit.
• ECM/PCM Failure: While rare, an internal fault within the Engine/Powertrain Control Module that affects the IAT Sensor 2 input circuit can cause this code. This should only be considered after all other possibilities have been meticulously ruled out.

How to Diagnose and Troubleshoot

Diagnosing P0098 requires systematic electrical testing and observation of live data. Always begin with a thorough visual inspection.

1. Visual Inspection:
   • Locate IAT Sensor 2 (refer to service manual for specific vehicle location, often in the intake manifold or charge pipe post-intercooler).
   • Inspect the sensor and its electrical connector for any visible damage, corrosion, bent pins, or loose connections.
   • Trace the wiring harness from the sensor back towards the ECM/PCM, looking for signs of chafing, cuts, melting, or rodent damage.
2. Scan Tool Data Analysis:
   • Connect an OBD-II scanner and retrieve any pending or stored DTCs and freeze frame data. The freeze frame data provides critical insights into engine conditions (RPM, engine load, coolant temp) at the moment the code was set.
   • Monitor the live data stream for IAT Sensor 2. With a “Circuit High” condition, the sensor reading will typically be stuck at an extremely low temperature value (e.g., -40°F or -40°C), regardless of actual ambient or operating temperatures. This is a strong indicator of an open circuit.
3. Digital Multimeter (DMM) Testing at Sensor Connector:
   • Ignition OFF: Disconnect the IAT Sensor 2 electrical connector.
   • Reference Voltage Check (Ignition ON): With the ignition ON, measure the voltage between the 5-volt reference pin on the harness side of the connector and a known good chassis ground. You should read approximately 5 volts. If not, investigate the reference voltage circuit from the ECM/PCM.
   • Ground Circuit Check (Ignition OFF): With the ignition OFF, measure the resistance between the ground pin on the harness side of the connector and the battery negative terminal. Resistance should be less than 5 ohms. High resistance indicates an open ground circuit.
   • Sensor Resistance Check (Ignition OFF): Disconnect the sensor. Measure the resistance across the two terminals of the IAT Sensor 2 itself. Compare this reading to the specified resistance-temperature chart for your vehicle’s IAT sensor (found in the service manual). At ambient temperature, there should be a measurable resistance value. An infinite resistance (open circuit) confirms a faulty sensor.
4. DMM Testing for Wiring Harness Integrity (ECM/PCM Disconnected):
   • Ignition OFF: Disconnect the negative battery terminal, then disconnect the ECM/PCM connector(s) that contain the IAT Sensor 2 wires.
   • Continuity Check: Measure the resistance of the signal wire between the IAT Sensor 2 connector (pin) and its corresponding pin at the ECM/PCM connector. Resistance should be less than 5 ohms. Repeat for the ground wire. High resistance or an open circuit indicates a break in the wiring.
   • Short to Ground Check: Measure resistance between the signal wire pin at the ECM/PCM connector and a known good chassis ground. Resistance should be infinite (open). Any low resistance indicates a short to ground.
   • Short to Voltage Check: Measure resistance between the signal wire pin at the ECM/PCM connector and any other power wires (e.g., 12V supply wires) within the harness. Resistance should be infinite.
5. Wiggle Test: While monitoring IAT Sensor 2 live data with the scan tool, gently wiggle the wiring harness and connector near the sensor and the ECM/PCM. Any sudden changes in the IAT reading or flickering voltage indicate an intermittent connection or wiring issue.

Recommended Repairs and Solutions

Based on the diagnostic findings, the following repairs are typically recommended:

• Replace IAT Sensor 2: If testing definitively confirms the sensor itself is faulty (e.g., open circuit or incorrect resistance), replacement is necessary. Always use a high-quality OEM or reputable aftermarket sensor to ensure accurate readings and system compatibility. Ensure the O-ring or seal is properly seated if applicable.
• Repair or Replace Wiring Harness: If diagnostic steps identify an open circuit, short to voltage, or significant damage in the wiring harness, perform a professional repair. This involves soldering and heat-shrinking damaged wires, or replacing sections of the harness as needed. For connector issues, pigtail connectors can often be spliced in. Ensure all repairs maintain waterproof integrity and proper strain relief.
• Clean Electrical Connectors: If corrosion is found on the sensor or harness connector terminals, carefully clean them using an electrical contact cleaner and a small brush. Ensure they are dry before reconnecting. Applying a small amount of dielectric grease can help prevent future corrosion.
• ECM/PCM Replacement: This is a very uncommon solution for P0098 and should only be pursued after all other components and wiring have been thoroughly tested and verified to be in good working order. If an ECM/PCM replacement is deemed necessary, it will typically require programming or coding to the vehicle’s specific parameters by a qualified technician.

After any repair, clear the DTCs using an OBD-II scan tool. Then, perform a comprehensive drive cycle under varying conditions to confirm that the code does not return and that the IAT Sensor 2 is providing accurate and consistent readings.