P00AC
Intake Air Temperature Sensor 1 Circuit Low Bank 2P00AC is a generic OBD-II powertrain diagnostic trouble code: Intake Air Temperature Sensor 1 Circuit Low Bank 2. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P00AC means
DTC P00AC is stored when the PCM detects that the signal voltage from the Bank 2 IAT Sensor 1 (IAT1) has fallen below the lower limit of the sensor's calibrated range — typically below approximately 0.1–0.2 V. For an NTC thermistor like the IAT sensor, very low signal voltage corresponds to near-zero resistance, which the sensor would only achieve at implausibly high temperatures (above 150 °C). In practice, a circuit-low condition almost always indicates a short to ground on the signal wire, rather than extreme heat, because the ground path pulls the voltage below what the PCM's internal pull-up resistor can sustain. The Bank 2 IAT1 sensor is typically positioned in the upstream air intake duct on the Bank 2 side and provides the PCM with ambient charge temperature data used to calibrate initial fuel enrichment and ignition timing. When the signal is shorted low, the PCM reads an impossibly hot intake temperature and may reduce fuel enrichment and retard ignition timing — the opposite of what is typically needed, especially during cold starts. This can produce lean stumbles, hard starting, and hesitation. The fault should be repaired promptly as lean operation under load can stress pistons and valves over time.
Common causes
Most-frequently reported root causes when P00AC is logged.
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1
Short to ground on the IAT1 signal wire — most common cause, pulls voltage below the PCM's lower threshold
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2
Failed IAT1 sensor with an internally shorted thermistor element causing near-zero resistance output
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3
Damaged wiring insulation where the signal wire contacts chassis ground, a grounded bracket, or the engine block
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4
Pinched wiring harness in a door, hood, or engine mount compressing the signal wire against ground
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5
Water intrusion creating a conductive path between the signal circuit and ground inside the connector
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6
Missing reference voltage from PCM (open 5 V supply) combined with an internal sensor path to ground
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7
PCM input pin shorted internally to ground (rare; diagnose last)
Symptoms drivers notice
How to diagnose P00AC
A typical diagnostic flow when this code is present.
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1
Retrieve P00AC with a scan tool; note freeze-frame data including IAT1 Bank 2 voltage and coolant temperature — a voltage near 0 V on a cold engine confirms a short-to-ground condition
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2
With ignition on, observe the live IAT1 Bank 2 voltage reading; if it reads at or below 0.1 V regardless of ambient temperature, the signal circuit is shorted to ground
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3
Unplug the IAT1 Bank 2 sensor connector; if the voltage returns to 5 V (or near) after unplugging, the fault is in the sensor itself (internal short); if voltage remains near 0 V with sensor unplugged, the fault is in the wiring between the connector and the PCM
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4
Visually trace the signal wire from the Bank 2 IAT1 sensor toward the PCM, checking for chafed insulation, pinch points, moisture entry points, or contact with chassis/engine metalwork
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5
With the sensor unplugged, use a multimeter in continuity mode between the signal wire and chassis ground — continuity confirms a short to ground in the harness; locate and repair the damaged section
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6
Measure the IAT1 sensor resistance across its terminals: near-zero ohms at room temperature confirms an internally shorted sensor requiring replacement
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7
After repairing the short or replacing the sensor, verify PCM reference voltage is restored to approximately 5 V on the signal wire, clear codes, and test drive to confirm the repair
Related powertrain codes
Frequently asked questions
What does 'Circuit Low' mean for P00AC?
"Circuit Low" means the PCM is reading a signal voltage at or near the bottom of its measurable range (close to 0 V). Because the IAT sensor is an NTC thermistor with a 5 V supply, a near-zero voltage implies the signal circuit resistance is near zero — pointing to either a shorted sensor or a signal wire touching ground somewhere in the harness.
Will P00AC make the engine run rich or lean?
It will typically cause lean operation. The PCM interprets very low IAT voltage as an extremely high intake air temperature. In response it reduces fuel enrichment and may retard ignition timing, because it thinks the air is less dense than it actually is. This is the opposite of what you want, especially during a cold start, and can cause hesitation, lean stumble, and in severe cases pinging under load.
How do I tell if the short is in the sensor or in the wiring?
Unplug the IAT1 Bank 2 sensor connector while monitoring the signal wire voltage with ignition on. If the voltage rises back toward 5 V after unplugging, the short is inside the sensor and the sensor should be replaced. If the voltage stays near 0 V after unplugging, the short to ground is in the wiring harness between the connector and the PCM, and you need to trace and repair the damaged wire.
Can P00AC and P00A8 appear at the same time?
Not on the same sensor simultaneously — P00A8 is a circuit-high fault and P00AC is a circuit-low fault for IAT sensors on Bank 2. However, they could appear together if one sensor circuit is shorted low while a different sensor circuit is open-high. Reviewing which specific sensor (IAT1 vs IAT2) each code references is essential before beginning diagnosis.
Disabling P00AC in software
RaceTune can permanently disable P00AC — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
ECU families we can disable P00AC on
We hold the DaVinci A2L disable definitions for these families, so the exact P00AC path and mask addresses are mapped. verified marks a confirmed disable definition. We support many more — upload your file and our identifier will match it automatically.
- Bosch EDC17CP57 verified
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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