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DTC code page

P0407: Exhaust Gas Recirculation Sensor B Circuit Low

Quick answer: The ECU sees the EGR Sensor B feedback signal stuck lower than expected, pointing toward a low-voltage feedback or reference issue rather than a pure flow complaint.

Drivers also search this fault as EGR sensor B low, EGR feedback B low voltage, EGR sensor B circuit low.

Severity: medium Family: powertrain Related paths: 8
Meaning

What P0407 usually means

P0407 narrows the EGR diagnosis to the Sensor B feedback side of the system. Depending on platform, Sensor B may be a second position channel, a differential-pressure-style feedback branch, or a dedicated EGR feedback signal the ECU uses to validate movement. A low reading can be caused by a biased sensor, missing reference voltage, poor ground, signal wire shorted low, or a valve that is physically parked in a position that makes the low reading look believable. The practical job is to decide whether the signal is lying or whether the valve really is not where the controller expects it to be.

Fast triage

Start here before chasing parts

  • Scan first: save freeze-frame and pending codes before clearing anything.
  • Confirm the complaint: compare the stored code with current drivability symptoms.
  • Use context: trims, live data, and related codes usually narrow the fault faster than guesswork.
  • Work simplest to hardest: leaks, connectors, maintenance items, and known patterns before expensive components.
Initial checks

What to check first

  • Read the actual feedback voltage first, because a true low signal and a mechanically closed valve can look similar until you compare command and feedback.
  • Inspect the connector and harness near the EGR unit before replacing parts, because heat and vibration make that area a common failure point.
  • Check whether P0403, P0404, or P0409 is also present, because companion codes help separate a hard circuit problem from a valve-behavior issue.
Driving risk

Can you keep driving?

P0407 is often still driveable, but rough idle, hesitation, or emissions-test failure can follow if the ECU no longer trusts EGR feedback. Fix it soon rather than chasing secondary drivability complaints later.

Moderate urgency: This code often allows short-term driving, but the right fix usually comes faster when you diagnose it early instead of waiting for more codes.
Symptoms

Common symptoms

Likely causes

Common causes behind this code

  • Sensor B feedback circuit shorted toward ground or dragged low by high resistance
  • Missing or unstable reference voltage feeding the EGR feedback circuit
  • Poor ground at the EGR valve or sensor assembly
  • Connector corrosion, spread terminals, or heat damage near the valve
  • Biased feedback sensor or internal failure inside the electronic EGR assembly

Cause phrases often tied to this code: low EGR feedback signal, short to ground, missing 5 volt reference, bad EGR sensor, poor sensor ground.

Diagnostic order

Suggested workflow

  1. Capture freeze-frame and note whether the code set at idle, cruise, or during an EGR self-test.
  2. Verify Sensor B reference voltage, ground quality, and signal continuity at the connector.
  3. Compare commanded EGR action with the Sensor B feedback trace if the scan tool supports it.
  4. Inspect the harness for chafing, oil contamination, or exhaust heat damage.
  5. After repair, confirm the feedback signal returns to a believable range and related EGR codes stay gone.
Avoid guesswork

Common mistakes

  • Replacing the full EGR valve before checking whether the signal is simply missing its reference or ground.
  • Treating P0407 like an automatic low-flow code instead of a feedback-circuit problem.
  • Ignoring intermittent harness faults that only appear when the engine rocks under load.
Repair path

Practical fix guidance

  • Repair the proven wiring, terminal, ground, or reference issue first before condemning the valve assembly.
  • If the sensor is integrated into the valve, verify the circuit feeds are correct before replacing the unit.
  • After the fix, road-test through idle and light cruise because EGR feedback faults often return only in the exact monitor window.
Vehicle context

Affected brands in this MVP

Brand hubs help broaden internal linking now and can evolve into make-specific diagnostic notes later.

Aliases and common searches

English phrases tied to P0407

Useful when the driver knows the wording but not the exact DTC yet.

  • EGR sensor B low
  • EGR feedback B low voltage
  • EGR sensor B circuit low
Related search intent

Queries this page can answer naturally

  • P0407 code meaning
  • what does P0407 mean
  • EGR sensor B circuit low symptoms
  • EGR feedback signal low
FAQ

Quick questions about P0407

Is P0407 the same as low EGR flow?

No. P0407 points at a low Sensor B feedback signal. The valve may still have a flow problem, but the code itself is about the circuit or feedback branch.

Can a missing 5-volt reference trigger P0407?

Yes. If the sensor loses its reference or ground, the feedback can read abnormally low even when the valve itself is not the root cause.

Why does P0407 sometimes come and go?

Because heat, vibration, and terminal tension problems can make the feedback signal fail only in certain operating conditions.