What Does P040C Mean?
The EGR temperature sensor A circuit is reporting a voltage that the ECM interprets as an abnormally low temperature. For NTC (negative temperature coefficient) thermistors, this typically means the sensor resistance is too high (open circuit or high-resistance fault), causing the ECM to see a low-temperature reading when it expects a higher one. The driver will not notice any drivability issues in most cases.
Common Causes
35%
Open circuit in the EGR temperature sensor A wiring — broken wire or disconnected connector
30%
Failed EGR temperature sensor with open internal element
20%
Corroded connector causing high resistance (effectively open) in the circuit
15%
ECM reference or ground circuit issue affecting temperature reading
Diagnostic Steps
1
Check the EGR temperature sensor PID — if reading -40F (-40C) or an impossibly low value, this confirms an open circuit (max resistance = lowest temperature reading for NTC sensors).
2
Disconnect the sensor and measure resistance across the terminals — at room temperature it should read approximately 2,000–3,000 ohms. An infinite (OL) reading means the sensor element is open.
3
If the sensor resistance is correct, check the wiring for continuity from the sensor connector to the ECM connector — check both the signal and ground wires. Resistance should be under 5 ohms.
4
Inspect the connector for corrosion, especially on vehicles in high-humidity or road-salt environments. The EGR area is prone to heat-related connector degradation.
5
Jumper the sensor terminals at the connector with a known resistance (e.g., 2,200 ohms) and verify the ECM reads a corresponding temperature — this confirms the circuit and ECM are functional.
Estimated Repair Cost
$50 - $200
Parts + labor, varies by vehicle and location
The EGR temperature sensor A circuit is reporting a voltage that the ECM interprets as an abnormally low temperature. For NTC (negative temperature coefficient) thermistors, this typically means the sensor resistance is too high (open circuit or high-resistance fault), causing the ECM to see a low-t...
The most common cause of P040C (Exhaust Gas Recirculation Temperature Sensor "A" Circuit Low) is: Open circuit in the EGR temperature sensor A wiring — broken wire or disconnected connector
Typical repair costs for P040C range from $50 to $200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive. This is a monitoring circuit fault only. No effect on engine performance or safety. The vehicle will fail emissions testing.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P040C to identify the root cause.
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Quick Info
Category
Powertrain
System
Emissions Control / EGR System
Difficulty
Type
Generic (SAE)
Recommended Tools
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