P0407 — Exhaust Gas Recirculation Sensor B Circuit Low

powertrain (engine/transmission)

Is it safe to drive?

Limited driving recommended P0407 alone does not normally require immediate stopping, but the EGR system may not operate correctly. Avoid heavy driving if the engine runs roughly, stalls, loses power, or shows other related trouble codes, and complete the circuit diagnosis promptly.

Typical symptoms

The check-engine light may illuminate with P0407 stored in the powertrain controller.
P0407 can cause the EGR controller to disable or limit exhaust-gas recirculation.
A rough idle, hesitation, or light surge may occur if the reduced EGR flow affects engine operation.
Exhaust temperatures may rise and catalyst performance can decline when P0407 prevents proper EGR control.
Some vehicles fail an emissions inspection because the reduced EGR operation can increase nitrogen-oxide readings.

Common causes

A short to ground in the EGR Sensor B signal circuit can force the voltage low and set P0407.
A faulty EGR Sensor B may pull its signal voltage below the manufacturer-specified threshold.
Corrosion, moisture, or damaged terminals in the EGR Sensor B connector can cause an intermittent low reading.
A low-reference or poor-ground condition at the powertrain control module can affect the Sensor B circuit.
Incorrectly repaired wiring near the EGR system may leave P0407 active even when the sensor itself is functional.

How to diagnose with an OBD scanner

Confirm P0407 with an OBD scanner Connect an ELM327-based scanner or AIScanAuto, read stored, pending, and permanent codes, and confirm that P0407 is currently reported. Review freeze-frame data for operating conditions when the fault was set.
Inspect the EGR Sensor B circuit Using the vehicle wiring diagram, locate EGR Sensor B rather than Sensor A or C. Inspect its connector, terminals, wire insulation, routing, and nearby grounds for corrosion, heat damage, chafing, or water intrusion.
Measure signal and reference voltage Back-probe the EGR Sensor B signal and reference pins with the wiring diagram in hand. Compare both voltages with manufacturer specifications; a signal below the specified low threshold confirms the circuit condition described by P0407.
Separate sensor and wiring faults Disconnect EGR Sensor B and check the signal and reference circuits for continuity to ground or an abnormal short. If the wiring and grounds pass, test or replace the sensor; do not assume the sensor is faulty solely because P0407 is present.
Repair and verification check Repair the damaged connector, harness, ground, or EGR Sensor B, then clear the code with the scanner. Recheck P0407 and Sensor B live data under the conditions that originally triggered the fault.

Approximate repair cost

A typical independent-shop estimate for EGR Sensor B diagnosis and replacement is USD 120–350. Harness or connector repair may add approximately USD 100–300 depending on access and damage. These figures are estimates and vary by region.

Common questions

Does P0407 always mean EGR Sensor B is defective?

No. P0407 can also result from a short to ground, connector damage, low reference voltage, or a poor control-module ground, so circuit testing is essential before replacing the sensor.

Is it safe to drive a vehicle with P0407?

Usually, yes, if the engine runs normally and no additional major fault codes are present. P0407 can reduce EGR operation, increase emissions, and cause drivability symptoms, so diagnosis should not be delayed.

Can ELM327 or AIScanAuto fully diagnose P0407?

They can confirm P0407, display freeze-frame information, and show available live data. Pin-level voltage testing, wiring checks, and access to manufacturer service information are still needed for a complete diagnosis.

Why does P0407 return after the EGR sensor is replaced?

A replacement sensor may not correct the fault if the actual cause is a shorted signal wire, damaged connector, poor ground, or low reference voltage. Clearing the code and monitoring the repaired circuit is essential.

When your scan tool displays P0407, the engine control module has identified that the exhaust gas recirculation system is behaving outside its designed parameters. P0407 translates to "Exhaust Gas Recirculation Sensor B Circuit Low," a powertrain fault code that points directly at the EGR sensor circuitry. The control unit watches this circuit constantly while the engine runs, and when the signal voltage drops below the minimum acceptable threshold for too long, it logs P0407 and illuminates the Check Engine light.

"Circuit low" is the key phrase here. It means the voltage on the EGR sensor B circuit is sitting near ground potential instead of within the normal operating range. This typically happens when a wire shorts to ground, insulation wears through and exposes bare metal, a sensor fails and drags the signal down, or power supply to the sensor is interrupted entirely. The ECU doesn't guess at the cause—it simply records the fault and flags it for you to investigate.

The module saves freeze frame data alongside P0407, capturing the exact engine speed, load, temperature, and vehicle speed at the moment the problem was detected. That snapshot is invaluable during diagnosis because it lets you recreate the driving conditions where the fault appears. Once the readings stay out of bounds for enough consecutive drive cycles, the code sets permanently until cleared and verified fixed.

Common Symptoms of P0407

Check Engine light remains illuminated
Engine runs roughly or stalls when idling
Hesitation and spark knock (pinging) when accelerating under load
Noticeable loss of engine power
Higher than normal NOx emissions at the tailpipe

What Causes P0407?

The most frequent culprit behind P0407 is a signal wire in the EGR harness that has shorted to ground—often caused by chafed insulation rubbing against metal surfaces. A failed EGR sensor B that can no longer produce a valid voltage signal also drops the circuit low. Other common causes include missing supply voltage to the sensor, a faulty EGR valve or integrated position sensor, heavy carbon deposits blocking the EGR valve pintle or intake passages, an ECM internal control circuit problem, a defective EGR solenoid or its wiring, and vacuum leaks in the EGR control plumbing.

How to Diagnose P0407

Plug in an OBD2 scanner, verify P0407 is stored, and record the freeze frame data—this shows engine conditions when the fault triggered.
Pull any related diagnostic trouble codes too. Co-occurring codes often point to the root cause. Also search for TSBs (technical service bulletins) for your specific make and model—manufacturers sometimes publish known fixes or calibration updates for recurring P0407 issues.
Inspect the wiring harness and connectors feeding the EGR system. Look for damaged insulation, broken pins, corrosion buildup, or loose terminals that could interrupt the signal.
Measure supply voltage at the EGR sensor B connector to confirm the module is providing power. Then check resistance from the signal circuit to ground—continuity (near-zero ohms) indicates a short to ground in the harness.
Use the scanner to command the EGR valve open and closed while monitoring position feedback and idle quality. A valve that responds poorly or not at all may be jammed or electrically failed.
Remove the EGR valve and inspect both the valve itself and the intake manifold passages for carbon buildup that could restrict flow.
Clear the code, perform a complete drive cycle that recreates the freeze frame conditions, and confirm P0407 does not return.

How to Fix P0407

Tackle the simplest and cheapest possibilities before replacing major components. Carbon cleaning of the EGR valve and passages typically runs $120–$350. Repairing damaged vacuum lines or wiring harness issues generally costs $80–$250. If the valve itself is faulty, replacement with a new or remanufactured unit runs $250–$650 including labor.

How Much Does It Cost to Fix P0407?

Depending on which part actually caused P0407, expect to pay between $80 and $650 for parts and labor at an independent shop. Cleaning the EGR valve is the least expensive repair and resolves the issue in many cases. Wiring or vacuum repairs fall in the middle range. Full EGR valve replacement is the costliest scenario. Getting an accurate diagnosis before purchasing parts is the smartest move—the most expensive fix is rarely the first one to try.

Can You Drive with P0407?

P0407 is generally safe to drive for short distances, but don't ignore it indefinitely. Expect rough idle, pinging under acceleration, and elevated exhaust emissions. Some vehicles may enter a reduced-power mode to protect the engine. If the car stalls repeatedly or runs extremely rough, treat it as urgent and schedule repairs promptly.