P0408 EGR valve position sensor B signal reads too high

EGR sensor B circuit high

Severity not verified — if the car runs badly, have it inspected

TroubleCodes.net says drivers usually notice little beyond the warning lamp, possibly a reduced-performance mode, but no source rates the code, so the severity is not verified.

Source: how we rate severity

P0408 in short

P0408 means the engine computer sees the signal from EGR position sensor B as too high. Wiring and connector faults are the most common cause, then the sensor itself or a sticking EGR valve. The car usually drives normally with only the check engine light on, but have it tested to protect emissions and fuel economy.

The computer watches the position sensor on the exhaust gas recirculation valve to know how far the valve is open. The PCM sees abnormally high voltage in the sensor B circuit. The delaware and troublecodes lists both define it as the EGR position sensor B circuit, high.

The letter B marks a second sensor or circuit, and which part that is depends on the engine, so the maker's information is needed to find it.

Wiring and the sensor itself are the first things to test. TroubleCodes.net adds that some Dodge, Chrysler, Jeep and Ram models have computer reprogramming bulletins for this code.

Most likely causes

These are general causes for this code across vehicles. None is specific to one make or model.

  1. Damaged, corroded or loose wiring or connector at the EGR position sensor

    Common general cause
    Why it ranks here
    TroubleCodes.net lists wiring and connector faults first, and a circuit voltage code is a circuit fault by definition.
    What would change this
    Rises if the harness shows chafing, corrosion or a loose pin. Falls if wiring and connector test clean.

  2. Failed EGR valve position sensor

    Common general cause
    Why it ranks here
    The code names the sensor B signal, and TroubleCodes.net lists a defective position sensor, including heat failure.
    What would change this
    Rises if wiring is good and the sensor signal stays out of range. Falls if the signal moves normally.

  3. Engine computer fault (some Dodge, Chrysler, Jeep and Ram models)

    Possible — needs testing
    Why it ranks here
    TroubleCodes.net says some Dodge, Chrysler, Jeep and Ram models are handled by bulletins that reprogram the engine computer; only the page was read, not the bulletins.
    What would change this
    Rises on those makes if wiring and sensor test good. Falls on other makes.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Read all stored codes and freeze-frame data, and use the maker's information to find which sensor is circuit B on your engine.

    Low riskTool: OBD-II scan tool

  2. With the engine off and cool, look over the EGR sensor connector and visible harness for damage, bent pins, corrosion or water.

    Low risk

  3. Have the sensor reference voltage, ground and signal measured with the key on, and the valve checked for free movement and carbon.

    Best left to a shopTool: digital multimeter, scan tool

    Warning:The EGR valve and its pipes get very hot after running, and probing connectors can short a circuit and damage the computer. Let the engine cool and leave this to a shop.

Symptoms

  • Check engine light on
  • Little or no change in how the car drives
  • Possible reduced performance and slightly worse fuel economy

How to fix

On your vehicle

Jeep

  • 2020–2021 · Wrangler

    Supported by vehicle data

    Jeep bulletin S2025000005 Rev. covers the check engine light with P0407 (EGR sensor B circuit low) or P0408 (EGR sensor B circuit high) set; Jeep bulletin 9004343 covers replacing the high pressure EGR valve because of P0407 or P0408, with a pointer to all published service information on diagnosis first. Whether it is still current is not verified.

  • S2025000005 Rev. (jeep)Status unverified

    MIL on with EGR sensor B circuit low or high, P0407 or P0408

    2020wrangler · issued · NHTSA 10187073

    Bulletin on check engine light illumination where P0407 (EGR sensor B circuit low) or P0408 (EGR sensor B circuit high) is set. Only the NHTSA summary was read, not the bulletin itself.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • 9004343 (jeep)Status unverified

    High pressure EGR valve replacement for P0407 or P0408

    2020–2021wrangler · issued · NHTSA 10187014

    Bulletin saying that anyone replacing the high pressure EGR valve because of P0407 or P0408 should first refer to all published service information on proper diagnosis. Only the NHTSA summary was read, not the bulletin itself.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Ram

  • 2020–2021 · 1500

    Supported by vehicle data

    Ram bulletin S2025000005 Rev. covers the check engine light with P0407 (EGR sensor B circuit low) or P0408 (EGR sensor B circuit high) set; Ram bulletin 9004343 covers replacing the high pressure EGR valve because of P0407 or P0408, with a pointer to all published service information on diagnosis first. Whether it is still current is not verified.

  • S2025000005 Rev. (ram)Status unverified

    MIL on with EGR sensor B circuit low or high, P0407 or P0408

    20201500 · issued · NHTSA 10187073

    Bulletin on check engine light illumination where P0407 (EGR sensor B circuit low) or P0408 (EGR sensor B circuit high) is set. Only the NHTSA summary was read, not the bulletin itself.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • 9004343 (ram)Status unverified

    High pressure EGR valve replacement for P0407 or P0408

    2020–20211500 · issued · NHTSA 10187014

    Bulletin saying that anyone replacing the high pressure EGR valve because of P0407 or P0408 should first refer to all published service information on proper diagnosis. Only the NHTSA summary was read, not the bulletin itself.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Dodge

  • 2010–2012 · Ram 1500

    Supported by vehicle data

    Dodge bulletin S2025000005 covers the check engine light with P0407 (EGR sensor B circuit low) or P0408 (EGR sensor B circuit high) set. Whether it is still current is not verified.

  • S2025000005Status unverified

    MIL on with EGR sensor B circuit low or high, P0407 or P0408

    2010–2012ram-1500 · issued · NHTSA 10223525

    Bulletin on check engine light illumination where P0407 (EGR sensor B circuit low) or P0408 (EGR sensor B circuit high) is set. Only the NHTSA summary was read, not the bulletin itself.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

No curated relationships for P0408 yet.

All Turbocharging, fuel pressure and EGR codes

P0408 questions

Can I drive with P0408?

TroubleCodes.net says most drivers notice little beyond the warning lamp, but the engine may limit performance. Have it checked rather than ignoring it.

Sources and review

  1. P0408 trouble code page — TroubleCodes.net
  2. S2025000005 Rev.: MIL on with EGR sensor B circuit low or high, P0407 or P0408 — Jeep
  3. 9004343: High pressure EGR valve replacement for P0407 or P0408 — Jeep
  4. S2025000005 Rev.: MIL on with EGR sensor B circuit low or high, P0407 or P0408 — Ram
  5. 9004343: High pressure EGR valve replacement for P0407 or P0408 — Ram
  6. S2025000005: MIL on with EGR sensor B circuit low or high, P0407 or P0408 — Dodge
  7. On-Board Diagnostic Trouble Codes (generic code title list) — Delaware Division of Motor Vehicles
Last reviewed
Written by
Saurabh K.
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