If your OBD-II scanner displays P0099, your vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected that the Intake Air Temperature (IAT) Sensor 2 signal is intermittent or erratic.
The generic OBD-II definition for P0099 is:
Intake Air Temperature Sensor 2 Circuit Intermittent
Unlike P0095, which indicates a general circuit fault, P0097, which identifies a low-voltage condition, or P0098, which indicates a high-voltage fault, P0099 means the PCM is losing communication with Intake Air Temperature Sensor 2 intermittently or receiving unstable voltage readings.
The signal may appear normal one moment and disappear, spike, or fluctuate the next.
Since the PCM relies on accurate intake air temperature information to calculate fuel delivery, ignition timing, emissions, and turbocharger boost control, intermittent sensor data can cause unpredictable engine performance and may eventually place the engine into a reduced-performance operating strategy.
Fortunately, P0099 is often caused by wiring problems, loose connectors, vibration-related faults, or a failing sensor rather than an expensive engine control module.
Alternate Manufacturer Definitions
Depending on the manufacturer or scan tool, P0099 may also appear as:
- Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic
- IAT Sensor 2 Intermittent Signal
- Intake Temperature Sensor 2 Intermittent
- Charge Air Temperature Sensor Intermittent
- Air Charge Temperature Sensor Intermittent
- Intake Air Sensor 2 Signal Intermittent
- Turbo Intake Temperature Sensor Intermittent
- Secondary Intake Air Temperature Sensor Circuit Intermittent
Although the wording varies, every definition refers to an unstable or intermittent electrical signal from Intake Air Temperature Sensor 2.
What Does the P0099 Code Mean?
The PCM constantly monitors Intake Air Temperature Sensor 2 to determine the temperature of the air entering the engine after it passes through the intake tract or intercooler.
This information is used to calculate:
- Fuel injector pulse width
- Ignition timing
- Air/fuel ratio
- Turbocharger boost management
- Engine load
- Emissions operation
When the PCM detects that Sensor 2 is producing a signal that suddenly disappears, spikes, or changes unpredictably without a corresponding change in engine operating conditions, it stores P0099 and illuminates the Check Engine Light.
Unlike a constant high- or low-voltage fault, an intermittent signal may only occur while driving over bumps, during engine vibration, or under specific temperatures.
How Intake Air Temperature Sensors Work
Most Intake Air Temperature sensors are Negative Temperature Coefficient (NTC) thermistors.
As intake air temperature changes:
The sensor resistance changes.
The return voltage changes.
The PCM converts that voltage into a temperature value.
Typical operation:
Cold Air
- Higher resistance
- Higher voltage
- Lower calculated temperature
Warm Air
- Lower resistance
- Lower voltage
- Higher calculated temperature
When the signal repeatedly drops out or changes unexpectedly, the PCM recognizes the fault as intermittent and stores P0099.
What Does “Circuit Intermittent” Mean?
A Circuit Intermittent code means the electrical signal is unstable.
Instead of remaining consistent, the circuit experiences brief interruptions.
Common causes include:
- Loose connector
- Broken wire inside insulation
- Poor terminal tension
- Vibration damage
- Water intrusion
- Corrosion
- Heat-damaged wiring
- Failing sensor
- Intermittent PCM connection (rare)
These faults are often difficult to duplicate because they may only occur while the vehicle is moving.
Where Is Intake Air Temperature Sensor 2 Located?
Location varies depending on engine design.
Common mounting locations include:
Charge Pipe
Many turbocharged engines install Sensor 2 in the aluminum charge pipe.
After the Intercooler
Many forced-induction engines measure charge air temperature after intercooler cooling.
Intake Manifold
Some naturally aspirated engines mount Sensor 2 directly in the intake manifold.
Integrated MAP/IAT Assembly
Many modern engines combine the MAP sensor and Intake Air Temperature sensor into one housing.
Always verify the correct sensor before beginning diagnosis.
How the PCM Detects P0099
The PCM continuously compares Intake Air Temperature Sensor 2 against several other engine sensors.
These include:
- Intake Air Temperature Sensor 1
- Ambient Air Temperature
- Engine Coolant Temperature
- Mass Air Flow Sensor
- Manifold Absolute Pressure Sensor
- Engine RPM
- Engine Load
If Sensor 2 repeatedly reports unrealistic temperature spikes or temporarily loses communication while the remaining sensors remain stable, the PCM stores P0099.
Difference Between P0095 Through P0099
These five diagnostic trouble codes identify different Intake Air Temperature Sensor 2 faults.
| Code | Description |
|---|---|
| P0095 | Intake Air Temperature Sensor 2 Circuit |
| P0096 | Intake Air Temperature Sensor 2 Performance |
| P0097 | Intake Air Temperature Sensor 2 Circuit Low |
| P0098 | Intake Air Temperature Sensor 2 Circuit High |
| P0099 | Intake Air Temperature Sensor 2 Circuit Intermittent |
Think of them like this:
P0095
General electrical fault.
P0096
Sensor performance problem.
P0097
Voltage too low.
P0098
Voltage too high.
P0099
Signal repeatedly comes and goes.
Symptoms of P0099
Symptoms often vary because the fault is intermittent.
Common symptoms include:
- Check Engine Light
- Occasional hesitation
- Rough idle
- Intermittent hard starting
- Poor fuel economy
- Reduced engine performance
- Engine stumbling
- Inconsistent throttle response
- Reduced turbocharger performance
- Random surging
- Rich or lean fuel mixture
- Failed emissions inspection
- Temporary reduced-power mode
Some vehicles may operate normally for days before symptoms suddenly return.
Can P0099 Cause Poor Fuel Economy?
Yes.
When Intake Air Temperature readings become unstable, the PCM may repeatedly adjust fuel delivery.
This can reduce fuel economy and increase emissions.
Can P0099 Cause Hard Starting?
Yes.
Intermittent temperature information may affect cold-start fuel calculations, causing:
- Long crank times
- Rough starts
- Temporary stalling
- Unstable idle after startup
Can P0099 Affect Turbocharger Performance?
Absolutely.
Turbocharged engines depend on accurate charge air temperature information.
An intermittent signal may cause the PCM to:
- Reduce boost
- Delay throttle response
- Limit engine torque
- Enter a protective operating mode
Can P0099 Cause Rough Idle?
Yes.
An unstable Intake Air Temperature signal can cause constantly changing fuel calculations, leading to:
- Rough idle
- RPM fluctuations
- Hesitation
- Engine vibration
Is P0099 Serious?
P0099 is generally considered a moderate-severity diagnostic trouble code.
Although many vehicles remain drivable, intermittent electrical faults often worsen over time.
Ignoring the problem may eventually result in:
- Poor engine performance
- Increased emissions
- Reduced fuel economy
- Additional sensor-related DTCs
- More difficult diagnosis later
Prompt diagnosis is recommended.
Can You Drive with P0099?
Usually, yes.
If the vehicle:
- Starts normally
- Runs smoothly most of the time
- Does not enter limp mode
- Has acceptable throttle response
Short-term driving is generally safe.
However, if drivability problems become frequent or severe, repairs should be completed immediately.
25 Common Causes of P0099
The most common causes include:
- Failing Intake Air Temperature Sensor 2
- Loose sensor connector
- Broken wiring inside insulation
- Heat-damaged wiring
- Connector corrosion
- Loose connector terminals
- Water intrusion
- Oil contamination
- Broken connector locking tab
- Vibration-related wiring damage
- Poor engine ground
- Chafed wiring harness
- Damaged PCM connector
- Rodent damage
- Faulty MAP/IAT combination sensor
- Improper aftermarket intake installation
- Intercooler service disturbing the harness
- Previous wiring repairs
- Charging system voltage fluctuations
- Faulty Ambient Air Temperature sensor causing correlation issues
- Faulty Engine Coolant Temperature sensor
- PCM software issue
- Internal PCM failure (rare)
- Low-quality aftermarket sensor
- Excessive engine vibration
One of the most common causes of P0099 is a loose electrical connector that temporarily loses contact as the engine moves under acceleration or while driving over rough roads, making this code particularly frustrating to diagnose.
Unlike P0097 or P0098, which indicate a constant low- or high-voltage condition, P0099 is triggered when the PCM detects that the Intake Air Temperature Sensor 2 signal repeatedly drops out, spikes, or becomes erratic. Because intermittent faults often disappear before testing begins, they are among the most challenging electrical problems to diagnose.
How to Diagnose the P0099 Code
Step 1: Verify the Code
Connect a professional OBD-II scan tool and record:
- Stored DTCs
- Pending DTCs
- Freeze-frame data
- Intake Air Temperature Sensor 1
- Intake Air Temperature Sensor 2
- Ambient Air Temperature
- Engine Coolant Temperature
- Battery voltage
Freeze-frame data often reveals whether the fault occurred during a cold start, highway driving, acceleration, or while the engine was under boost.
Step 2: Check for Additional Trouble Codes
P0099 commonly appears with:
- P0095 Intake Air Temperature Sensor 2 Circuit
- P0096 Intake Air Temperature Sensor 2 Performance
- P0097 Intake Air Temperature Sensor 2 Circuit Low
- P0098 Intake Air Temperature Sensor 2 Circuit High
- P0101 Mass Air Flow Sensor Performance
- P0106 MAP Sensor Performance
- P0111 Intake Air Temperature Sensor Performance
- P0112 Intake Air Temperature Circuit Low
- P0113 Intake Air Temperature Circuit High
- P0114 Intake Air Temperature Circuit Intermittent
Related intake and airflow codes often help narrow down the source of the fault.
Step 3: Perform a Visual Inspection
Inspect the complete Intake Air Temperature Sensor 2 circuit.
Look for:
- Loose connectors
- Broken locking tabs
- Chafed wiring
- Melted insulation
- Oil contamination
- Water intrusion
- Corrosion
- Rodent damage
Many intermittent faults can be identified during a careful visual inspection.
Step 4: Verify Sensor Location
Depending on the vehicle, Intake Air Temperature Sensor 2 may be located:
- After the intercooler
- In the charge pipe
- Inside the intake manifold
- Integrated into the MAP sensor
Always verify the correct sensor before beginning repairs.
Step 5: Compare Cold Engine Readings
Allow the engine to cool completely.
Before starting the engine, compare:
- Intake Air Temperature Sensor 1
- Intake Air Temperature Sensor 2
- Ambient Air Temperature
All three readings should be nearly identical.
Large differences may indicate an intermittent sensor or wiring fault.
Step 6: Inspect the Connector
Disconnect the sensor connector.
Inspect for:
- Bent terminals
- Loose terminal tension
- Corrosion
- Moisture
- Dirt
- Broken locking clips
Loose connectors are among the leading causes of P0099.
Step 7: Verify the 5-Volt Reference
Using a digital multimeter:
Verify the PCM is supplying approximately:
5 volts
Compare readings to factory specifications.
Step 8: Verify Ground Integrity
Inspect:
- Engine grounds
- Chassis grounds
- PCM grounds
Poor grounds can create unstable sensor signals.
Perform voltage-drop testing whenever possible.
Step 9: Test Sensor Resistance
Disconnect the sensor.
Measure resistance across the terminals.
Resistance should change smoothly as the sensor temperature changes.
Sudden jumps indicate internal sensor failure.
Step 10: Perform a Wiggle Test
Reconnect the sensor.
Monitor live scan tool data while gently moving:
- Sensor connector
- Wiring harness
- Charge pipe wiring
- PCM harness
Watch for:
- Temperature spikes
- Signal dropouts
- Sudden changes
This is often the fastest way to locate an intermittent fault.
Step 11: Inspect Wiring Near Heat Sources
Inspect wiring routed near:
- Turbochargers
- Exhaust manifolds
- Catalytic converters
- Heat shields
- Charge pipes
Repeated heating and cooling cycles can break wiring internally while leaving the insulation intact.
Step 12: Check for Internal Wire Breaks
Flex the harness by hand.
Intermittent internal wire breaks often occur where the harness bends repeatedly.
The outside of the wire may appear normal even when the conductor inside has fractured.
Step 13: Inspect the Sensor
Remove Intake Air Temperature Sensor 2.
Check for:
- Cracked housing
- Oil contamination
- Dirt buildup
- Damaged sensing element
Replace the sensor if damage is found.
Step 14: Inspect the Intake System
Inspect for:
- Loose charge pipes
- Vacuum leaks
- Damaged intercooler hoses
- Improper aftermarket installations
Although P0099 is primarily electrical, intake system issues may contribute to unstable sensor readings.
Step 15: Test Circuit Continuity
Disconnect:
- PCM connector
- Sensor connector
Measure continuity across each wire.
Intermittent wiring may require flexing the harness during testing.
Step 16: Inspect MAP/IAT Combination Sensors
Many vehicles combine:
- MAP Sensor
- Intake Air Temperature Sensor
If equipped, verify both sensor values.
Replace the assembly if either sensor fails testing.
Step 17: Verify Charging System Voltage
Inspect:
- Battery voltage
- Alternator output
- Charging system stability
Voltage fluctuations may affect multiple engine sensors.
Step 18: Inspect PCM Connectors
Disconnect the PCM following factory procedures.
Inspect for:
- Loose terminals
- Corrosion
- Moisture
- Damaged pins
PCM connector problems are uncommon but should not be overlooked.
Step 19: Review Technical Service Bulletins (TSBs)
Some manufacturers have issued TSBs involving:
- Improved connectors
- Updated wiring harnesses
- PCM software updates
- Revised Intake Air Temperature sensors
Always check for manufacturer updates before replacing expensive components.
Step 20: Monitor Live Data During a Road Test
Observe Intake Air Temperature Sensor 2 while driving.
Monitor during:
- Idle
- Moderate acceleration
- Highway cruising
- Heavy engine load
- Turbocharger boost
Look for sudden temperature spikes or signal loss.
Step 21: Compare Sensor 1 and Sensor 2
Small differences are normal.
Large or rapidly changing differences usually indicate:
- Wiring faults
- Loose connectors
- Sensor failure
Step 22: Inspect Aftermarket Modifications
Inspect for:
- Cold air intake kits
- Turbocharger upgrades
- Intercooler upgrades
- Custom wiring
- Engine tuning modifications
Improper installations frequently create intermittent wiring problems.
Step 23: Clear the Code
After repairs:
- Clear stored DTCs
- Restart the engine
- Monitor live data
Verify stable Intake Air Temperature readings.
Step 24: Perform a Road Test
Drive under various operating conditions:
- Idle
- Stop-and-go traffic
- Highway speeds
- Moderate acceleration
- Full operating temperature
Confirm the intermittent fault no longer occurs.
Step 25: Confirm the Repair
Before returning the vehicle:
Verify:
- No stored codes
- No pending codes
- Stable Intake Air Temperature Sensor readings
- Normal fuel trims
- Proper throttle response
- No Check Engine Light
Common Repairs for P0099
Depending on the diagnosis, repairs may include:
- Replacing Intake Air Temperature Sensor 2
- Repairing broken wiring
- Replacing damaged connectors
- Cleaning corroded terminals
- Repairing loose wiring harnesses
- Replacing MAP/IAT combination sensors
- Securing loose engine harnesses
- Updating PCM software
- Repairing poor ground connections
- Replacing the PCM (rare)
Estimated Repair Costs
| Repair | Typical Cost |
|---|---|
| Connector repair | $75–$250 |
| Wiring repair | $100–$350 |
| Intake Air Temperature Sensor | $50–$250 |
| Sensor replacement with labor | $125–$400 |
| MAP/IAT combination sensor | $150–$500 |
| Wiring harness repair | $150–$500 |
| PCM software update | $100–$250 |
| PCM replacement | $900–$2,500+ |
Actual repair costs vary by vehicle manufacturer, labor rates, and whether OEM or aftermarket parts are used.
Common Diagnostic Mistakes
Avoid these common mistakes:
- Replacing the sensor before performing a wiggle test
- Ignoring loose connector terminals
- Overlooking broken wires hidden inside insulation
- Skipping live-data monitoring during a road test
- Replacing the PCM too early
- Ignoring aftermarket intake modifications
- Failing to inspect heat-damaged wiring
- Overlooking poor engine grounds
- Ignoring Technical Service Bulletins
- Assuming intermittent faults will always appear while the vehicle is stationary
Most P0099 repairs involve connectors or wiring, not failed engine computers.
Manufacturer-Specific Notes
Ford
EcoBoost engines commonly develop intermittent wiring faults near the turbocharger and intercooler piping due to heat and vibration.
General Motors
Many GM engines use a combined MAP/IAT sensor assembly. Monitor both sensor values for intermittent signal loss before replacing the assembly.
Toyota & Lexus
Connector corrosion and loose terminal tension are common causes of intermittent intake air temperature faults.
Honda & Acura
Inspect wiring around aftermarket intake systems and intercooler upgrades, which frequently strain the factory harness.
Nissan & Infiniti
Inspect intake harness routing carefully for chafing against engine brackets or intake tubing.
BMW & MINI
Charge Air Temperature sensor wiring is commonly exposed to heat and oil contamination. Inspect connectors carefully.
Volkswagen & Audi
Verify sensor operation using live data while performing a wiggle test on the integrated MAP/IAT connector.
Mercedes-Benz
Inspect wiring routed near turbocharger plumbing where vibration and high temperatures can create intermittent open circuits.
Hyundai & Kia
Check connector security and inspect wiring for vibration-related damage near the intake manifold.
Diesel Engines
Turbocharged diesel engines commonly experience intermittent charge air temperature sensor faults due to vibration around intercooler piping and charge air plumbing.
Frequently Asked Questions
What does P0099 mean?
P0099 indicates the PCM has detected an intermittent or unstable electrical signal from Intake Air Temperature Sensor 2.
Is P0099 serious?
Generally, P0099 is considered a moderate-severity code. The vehicle often remains drivable, but intermittent faults tend to worsen over time and should be repaired promptly.
Can I drive with a P0099 code?
Yes, in most cases. However, if the engine develops hesitation, reduced-power mode, or poor drivability, repairs should be completed as soon as possible.
Does P0099 always mean the sensor is bad?
No. Loose connectors, broken wiring, poor grounds, vibration damage, or a failing MAP/IAT combination sensor commonly trigger this code.
Can vibration cause P0099?
Yes. Engine movement and road vibration frequently expose loose connectors or broken wires that temporarily interrupt the sensor signal.
Can aftermarket intake systems trigger P0099?
Absolutely. Improperly routed or stretched wiring during intake installation is a common cause of intermittent sensor faults.
How much does it cost to repair P0099?
Repair costs typically range from $75 for connector repairs to more than $2,500 for rare PCM replacement, though PCM failures are uncommon.
Will clearing the code fix P0099?
No. Clearing the code only removes the stored DTC temporarily. The underlying intermittent electrical fault must be repaired before the code will remain cleared.
Can a scan tool identify the exact problem?
A scan tool is extremely helpful for monitoring live data, but intermittent electrical faults often require physical inspection, wiggle testing, and multimeter testing to locate.
What is the difference between P0099 and P0098?
P0098 indicates a constant high-voltage condition, while P0099 indicates the sensor signal is unstable or intermittently lost.
Preventative Maintenance
To reduce the likelihood of P0099:
- Inspect intake sensor connectors during routine maintenance.
- Secure wiring away from turbochargers and exhaust components.
- Replace damaged connector locking tabs.
- Repair oil leaks before they contaminate electrical connectors.
- Keep electrical connections clean and dry.
- Inspect aftermarket intake installations for strained wiring.
- Protect wiring with heat-resistant loom where appropriate.
- Address Check Engine Light warnings promptly before intermittent faults become more difficult to diagnose.
Routine inspection of the intake system and engine wiring harness can significantly reduce the risk of intermittent Intake Air Temperature Sensor faults.
Final Thoughts
The P0099 Intake Air Temperature Sensor 2 Circuit Intermittent code indicates that the ECM or PCM has detected an unstable electrical signal from the secondary intake air temperature sensor. Unlike constant high- or low-voltage faults, intermittent problems often occur only under specific driving conditions, making them more difficult to diagnose.
A systematic approach that includes inspecting the wiring harness, testing connectors, monitoring live scan tool data, performing wiggle tests, and verifying proper sensor operation will usually identify the root cause while preventing unnecessary replacement of otherwise functional components.
