|Trouble Code||Fault Location||Probable Cause|
|P0099||Intake air temperature (IAT) sensor 2 -circuit intermittent/erratic||Wiring, poor connection, IAT sensor, ECM|
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What Does Code P0099 Mean?
To get more power out of a set engine displacement, engine designers have come up with a number of ways, forced induction being one of them. In the intake, a compressor forces more air into the cylinders than they could normally suck in on their own. Turbochargers use exhaust gas flow to spin up the compressor, while superchargers use a belt-driven compressor, with similar results. Some forced-induction engines may use more than one turbocharger or a combination of turbocharger and supercharger.
Forcing more air into the cylinder, which is why it’s called “forced induction,” results in more oxygen for combustion, for which the engine control module (ECM) injects more fuel, resulting in more power. Overall, the addition of forced induction to an engine can generate upwards of 40% more power than a naturally-aspirated engine of the same displacement. One particular turbocharged 1.8 ℓ engine may produce 130 hp, while a turbocharged version of the same engine could produce up to 220 hp, a 70% increase in maximum power.
As with non-forced-induction engines, the ECM on a forced-induction uses a number of sensor readings to meter fuel injection and modulate ignition timing and variable valve timing, such as air flow and air temperature. Additionally, charged engines may have a few dedicated sensors, such as those measuring boost pressure and intake air temperature (IAT), which the ECM uses to tune fuel trim. If intake air temperature is too high, this could result in increased cylinder temperatures and excessive NOx (nitrogen oxides) emissions, so the ECM can reduce boost pressure if required.
Forced-induction engines have two IAT sensors. Usually, IAT or IAT1 refer to the sensor measuring air temperature coming into the mass air flow (MAF) meter. Because air temperature increases under compression, from the turbocharger or supercharger, sensor IAT2 is used to measure air temperature after just after the compressor. If the ECM detects a problem with IAT2, such as temperature or voltage out of specification, it will illuminate the malfunction indicator lamp (MIL) and store a diagnostic trouble code (DTC), P0099 Intake Air Temperature Sensor 2 Circuit Intermittent/erratic, in memory.
What are the common causes of code P0099 ?
Depending on year, make, and model, DTC P0099 may have number of causes. Here are some of the most common.
- ECM Programming – A number of TSBs referencing P0099 have been put out on a number of different makes and models, usually requiring reflashing of the ECM. This can only be done at the dealer service center.
- Poor Charge Cooling – Intercoolers and cooling systems are designed to reduce intake air temperature to improve combustion after charging. If the intercooler airflow is restricted or the coolant pump is compromised, overheating may result, which the ECM may interpret as a sensor problem. One particular Land Rover TSB references poor installation of the supercharger cooling pump, which would result in the pump running backwards. Repair included an ECM reflash, new pump, and rewiring the connector.
- Weather – Some manufacturers set P0099 for temperature correlations, such as requiring that IAT, IAT2, and CAC (charge air cooler) temperature be within 30 °F (16.7 °C) after 6 hours’ cold soak. In certain circumstances, the ECM may misinterpret these temperature readings as a problem. Some of the ECM reflashes may address this issue.
What are the symptoms of code P0099 ?
Aside from the MIL, and depending on failure mode, you may note poor engine performance, particularly on acceleration, though you may not notice anything while cruising or at low speeds. Some ECMs may internally substitute a certain temperature reading in its calculations, which may enable the vehicle to run, although you may still experience rough idle, hesitation on acceleration, perhaps a random misfire.
How do you troubleshoot code P0099 ?
Because IAT2 is a simple thermistor, diagnosis is fairly straightforward, requiring a DVOM (digital volt-ohm meter) or a scan tool with live data streaming. First, make sure connector IAT2 is firmly seated, with no bent or backed-out pins, corrosion, or evidence of water entry. Look for obvious wire harness damage, such as poor routing, chafing, or rodent damage. (An in-depth discussion of IAT sensor diagnosis can be found at DTC P0112, as well.)
- Scan Tool – This is the easiest way to check for proper IAT2 readings. With KOEO (key on engine off), watch IAT and IAT2 readings. With the engine off, both IAT and IAT2 should read about the same, at least within a few degrees of one another.
- Wiggle the connector and see if IAT2 changes. It shouldn’t. If it does, suspect a pin, connector, or harness problem. Proceed to DVOM Harness Check and repair as necessary. If IAT2 is reading properly, suspect an intermittent sensor or harness problem, possibly an ECM problem.
- If IAT2 reads something unusual, -30 °F or 300 °F, suspect a sensor or circuit problem. Disconnect IAT2. If the reading doesn’t change, suspect a circuit problem. If the reading changes, suspect a sensor problem. Repair or replace as necessary.
DVOM Sensor Check – To check a three-wire IAT2, maintain KOEO and backprobe the connector. Check for 5 V reference and a variable signal voltage, comparing it to the temperature / voltage chart in your repair manual. To check a two-wire IAT2, turn the key off and disconnect IAT2. Measure resistance across the sensor terminals and compare it to the current temperature and a temperature / resistance chart, which you can find in your repair manual.
- If the voltage / resistance is incorrect, suspect a sensor problem. Replace as needed.
- If voltage / resistance is correct, recheck at different temperatures, such as by putting the sensor in boiling or icy water. If the sensor still checks out, suspect a harness problem.
- DVOM Harness Check – To check the harness between the ECM and IAT2, turn the key off and disconnect the ECM connector. From the ECM connector, use your DVOM to check resistance in comparison with the temperature resistance chart, located in the repair manual.
- If resistance is as specified, suspect an intermittent problem, perhaps a loose connector or broken wire. Watch your resistance readings as you wiggle the connector and wire harness.
- If resistance is not as specified, disconnect IAT2 and recheck.
- If resistance changes, suspect a defective sensor. Replace as needed.
- If resistance doesn’t change, suspect a wire harness problem. Check for short circuits between power, ground, and signal wires, as well as body ground. Repair as necessary.
- If you cannot find any problems at all, that is, the circuits are sound and IAT2 is operating properly, you may have an intermittent problem, overheating issue, or a fluke. Before condemning the sensor or ECM, check with your dealer service center to see if any updated parts or ECM programming addresses your concern.
Codes Related to P0099
- P0095 Intake Air Temp. Sensor 2 Circuit
- P0096 Intake Air Temp. Sensor 2 Circuit Range/Performance
- P0097 Intake Air Temp. Sensor 2 Circuit Low
- P0098 Intake Air Temp. Sensor 2 Circuit High
- P0099 Intake Air Temp. Sensor 2 Circuit Intermittent/Erratic
- P0110 Intake Air Temp. Circuit
- P0111 Intake Air Temp. Circuit Range/Performance Problem
- P0112 Intake Air Temp. Circuit Low Input
- P0113 Intake Air Temp. Circuit High Input
- P0114 Intake Air Temp. Circuit Intermittent
- P0127 Intake Air Temp. Too High