What is EGR 'Sensor B' — is it the same as the EGR valve?

Not usually. 'Sensor A' (codes P0405/P0406) is almost always the EGR valve's position-feedback potentiometer. 'Sensor B' is the second EGR feedback channel, and on many platforms that's a dedicated EGR gas temperature sensor mounted in the exhaust-recirculation path — a separate part from the valve. That's why P0407 most often points at a temperature sensor rather than the valve itself. Some platforms do use Sensor B as a second position channel inside the valve, so confirming your engine's design is the important first step.

What does the EGR temperature sensor actually do?

It measures the temperature of the exhaust gas being recirculated back into the intake. The PCM uses that reading to confirm the EGR system is genuinely flowing hot exhaust when it commands the valve open — if the valve opens but the temperature doesn't rise, the system isn't actually flowing. It's a verification sensor, which is why losing it (P0407) takes EGR out of proper closed-loop monitoring even though the engine keeps running on a default strategy.

Can I keep driving with P0407?

Generally yes. The engine runs normally because the PCM falls back to a safe EGR strategy when it loses the feedback signal. The downsides are a small fuel-economy penalty and a guaranteed emissions-test failure. The reason not to ignore it indefinitely is that EGR temperature feedback is part of how the system self-checks, and with it offline a developing EGR flow problem can go unnoticed until it becomes a bigger driveability or emissions issue.

OBD-II trouble code

P0407: Exhaust Gas Recirculation Sensor 'B' Circuit Low

Q: How much does it cost to fix P0407?

If it's a standalone EGR temperature sensor, figure $90-420 installed — the part is $25-130 and labor depends on how buried the sensor is in the EGR tubing. A connector or wiring repair can be cheaper at $50-250. If your platform uses Sensor B as a second valve position channel and the valve has failed internally, you're looking at EGR valve replacement in the $300-600+ range. Identifying which type of sensor you have before buying parts is what keeps the cost down.

The EGR 'B' feedback signal is reading too low. On the platforms where this code matters most, Sensor B is a dedicated EGR gas temperature sensor rather than a valve position channel — which is why the primary fix here is the temperature sensor, not the valve.

Quick facts

System: Powertrain
Category: Emissions / Other
Severity: Medium severity
Drivable: Usually safe to drive short-term
Repair cost range: $50 – $600
DIY difficulty: Intermediate DIY

What does P0407 mean?

P0407 is the low-input member of the EGR 'Sensor B' pair, and understanding it starts with knowing what 'Sensor B' actually is on your engine. Where 'Sensor A' (P0405/P0406) is almost always the EGR valve's position-feedback potentiometer, 'Sensor B' is the second EGR feedback channel — and on a large share of the platforms that throw this code, that second channel is a dedicated EGR gas temperature sensor. This sensor sits in the EGR flow path and measures the temperature of the recirculated exhaust, which the PCM uses to confirm that the EGR system is actually flowing hot exhaust gas when it commands the valve open. That's a different part from the valve itself, which is exactly why this page leads with the temperature sensor as the primary repair.

P0407 sets when the Sensor B signal voltage falls below the PCM's minimum threshold. For an EGR temperature sensor — which is a thermistor, like a coolant or intake-air sensor — low voltage typically reads as very high temperature, and the fault usually means the signal has shorted to ground, the sensor has failed internally, or the connector has corroded in the hot environment near the EGR passage. Because EGR temperature sensors live in one of the harshest thermal spots on the engine, heat-related connector and sensor failures are common.

The practical impact is mild. Losing the EGR temperature signal doesn't stop the engine — the PCM falls back to a default strategy — but it does take the EGR system out of proper closed-loop monitoring, which costs a little fuel economy and will fail an emissions inspection. The reason to fix it promptly is that EGR temperature feedback is part of how the PCM verifies the system is working at all, and an unmonitored EGR system can mask a real flow problem that builds up later.

If your platform instead uses Sensor B as a second position channel rather than a temperature sensor, the repair shifts toward the EGR valve — which is why the valve replacement is offered as the secondary path. Confirm which architecture you have before ordering parts.

Common causes

Failed EGR gas temperature sensor (thermistor shorted internally)
Signal wire shorted to ground on the Sensor B circuit
Corroded connector in the hot zone near the EGR passage
Open or high-resistance ground affecting the temperature-sensor reading
On position-channel platforms, a failed second position-feedback element in the EGR valve
Harness chafe damage near the exhaust manifold or EGR tube
Connector left unseated after EGR or exhaust service
Aftermarket sensor of incorrect resistance specification

Symptoms

Check engine light on with P0407 stored
Mild reduction in fuel economy
Engine usually runs normally — EGR defaults to a safe strategy when feedback is lost
Possible light hesitation on platforms where EGR ties to throttle control
Failed emissions inspection
No temperature-related driveability change the driver would notice directly

Diagnostic steps

1.Determine whether Sensor B on your engine is an EGR temperature sensor or a second valve position channel — this decides whether you're chasing a standalone sensor or the valve.
2.Inspect the Sensor B connector for heat-related corrosion, melted insulation, or pushed-back pins — the EGR zone runs hot and connectors suffer.
3.Pull all codes. P0407 alone is the Sensor B circuit case; P0407 with P0408 points at shared wiring; P0407 with valve codes broadens it.
4.For a temperature-sensor design, measure resistance across the sensor terminals and compare to the temperature/resistance spec — a near-zero reading confirms an internal short.
5.Back-probe the signal wire while wiggling the harness to expose a short-to-ground along the run near the manifold.
6.Check the sensor ground for continuity and low resistance.
7.If the sensor and wiring test good on a position-channel platform, the fault is in the EGR valve's feedback element — replace the valve and confirm feedback tracks after.

Repair cost

$50 – $600

If Sensor B is a standalone EGR temperature sensor, the part runs $25-130 and labor is 0.5-2.0 hours depending on how buried the sensor is in the EGR tubing — roughly $90-420 installed. A connector or wiring repair can be cheaper, $50-250. If your platform uses Sensor B as a second valve position channel and the valve's internal feedback has failed, you're into EGR valve replacement at $300-600+. Confirming the architecture first is what keeps a cheap sensor job from being mistaken for a valve replacement.

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DIY vs shop

This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.

Related codes

P0408 P0405 P0406 P0404 P0403 P0401