P0099 medium Severity

P0099: Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic

May cause reduced engine performance, poorer fuel efficiency, irregular idle, and MIL illumination

Overview

OBD-II code P0099 indicates that the powertrain control module (PCM) has detected an intermittent or erratic signal from the second Intake Air Temperature (IAT) sensor circuit, affecting air-fuel metering and engine performance.

Common Symptoms

  • Check Engine Light/MIL illuminated
  • Decreased fuel economy
  • Reduced engine performance or hesitation
  • Rough or irregular idle

Most Common Causes

Open or shorted Intake Air Temperature (IAT) sensor #2 wiring/connectors high

Faulty or intermittent electrical connections can produce erratic signals

Faulty Intake Air Temperature (IAT) sensor #2 high

Sensor internal failure can generate unstable readings

Clogged air filter or cracked intake duct affecting IAT readings medium

Distorted airflow can cause inconsistent temperature measurements

Faulty Mass Air Flow (MAF) sensor medium

MAF issues can sometimes be related but secondary to IAT circuit faults

PCM/ECM malfunction low

Rare cause if all sensor systems and wiring test good

Diagnostic Steps

  1. Connect OBD-II scanner and confirm P0099 with freeze frame data
    Expected: Code P0099 present and stored
    Interpretation: Confirms intermittent/erratic IAT sensor #2 circuit fault
  2. Perform visual inspection of IAT sensor #2 wiring, connectors, and intake air path
    Expected: No loose, corroded, broken wires or damaged connectors
    Interpretation: If faults found, repair wiring or connectors and re-test
  3. Measure sensor reference voltage and ground at IAT #2 connector with multimeter
    Expected: Stable reference voltage (typically ~5V) and good ground
    Interpretation: Absence indicates circuit supply/ground issue
  4. Test IAT sensor resistance/voltage output vs expected values at different temperatures
    Expected: Resistance/voltage changes smoothly with temperature
    Interpretation: Non-plausible readings suggest sensor replacement
  5. Inspect air filter and intake ducts for blockage/cracks
    Expected: Clean filter and intact duct
    Interpretation: Obstructions or leaks can skew sensor readings

Repair Solutions

Repair or replace wiring and connectors for IAT sensor #2 medium
Estimated Cost: $20 - $150

Connector cleaning and wiring repair often resolves intermittent faults

Replace Intake Air Temperature (IAT) sensor #2 easy
Estimated Cost: $30 - $200

Sensor replacement if out of spec or damaged

Replace Mass Air Flow (MAF) sensor if related issues found medium
Estimated Cost: $100 - $400

Only if diagnostics show MAF faults

PCM/ECM repair or reprogramming hard
Estimated Cost: $300 - $1200

Rare and only if diagnostics confirm control module fault

Common Misdiagnoses

Avoid these common diagnostic mistakes:

  • Incorrectly diagnosing fuel pressure or unrelated sensor codes as P0099 cause

Frequently Asked Questions

What is the definition of the P0099 engine code?

Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic is the standard definition for P0099. This diagnostic code is triggered when the ECU detects a problem in the Air Intake.

Can P0099 cause engine damage?

This is a medium priority issue. May cause reduced engine performance, poorer fuel efficiency, irregular idle, and MIL illumination

What are the symptoms of P0099?

The most typical signs are: Check Engine Light/MIL illuminated, Decreased fuel economy, Reduced engine performance or hesitation.

Why is my car throwing a P0099 code?

The most common causes are: Open or shorted Intake Air Temperature (IAT) sensor #2 wiring/connectors, Faulty Intake Air Temperature (IAT) sensor #2, Clogged air filter or cracked intake duct affecting IAT readings.

Repair cost breakdown for P0099

It depends on what needs to be fixed. Repair or replace wiring and connectors for IAT sensor #2 repairs are cheaper (~$150), while PCM/ECM repair or reprogramming repairs are on the higher end (~$1200).

Is P0099 a generic or manufacturer-specific code?

Yes, P0099 is a generic code that applies to all OBD-II compliant vehicles, including Ford, Toyota, Honda, Chevrolet, Nissan, Dodge, BMW, and more.

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