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DTC codes / Jaguar codes / P1408

P1408 · JaguarExhaust Gas Recirculation Thermister

P1408 on a Jaguar indicates that the engine control module has detected an implausible signal from the exhaust gas recirculation thermistor, which is the temperature sensor integrated into the EGR valve or EGR passage. The computer compares this temperature reading against expected values during EGR operation and flags the code when the signal falls outside the valid range or does not change as expected.

SystemPowertrain
Code typeJaguar specific
SeverityMedium
Fix difficultyIntermediate
AreaAuxiliary emission controls

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms
  • Rough idle or stumbling when the engine is cold, particularly on V6 and V8 Jaguar engines
  • Slight hesitation or surge during light acceleration when the EGR valve opens
  • Increased exhaust emissions that may cause a failure during an emissions inspection
  • In rare cases, a drop in fuel economy if the EGR system remains open or closed incorrectly

Common causes, most likely first

  1. Failed EGR thermistor (temperature sensor) internal open or short circuit
  2. Corroded or damaged electrical connector at the EGR valve or sensor
  3. Chafed or broken wiring between the EGR thermistor and the engine control module
  4. Carbon buildup on the thermistor tip, insulating it from exhaust gas flow
  5. Sticking or clogged EGR valve preventing proper gas flow past the sensor
  6. Faulty engine control module software or internal driver circuit (less common)

How to diagnose and fix it

  1. Connect a Jaguar-compatible scan tool and read live data for the EGR thermistor temperature to verify the signal is stuck or erratic
  2. Visually inspect the EGR valve and thermistor connector for corrosion, loose pins, or damaged insulation
  3. Check the resistance of the thermistor with a multimeter and compare to the manufacturer's temperature-resistance chart
  4. Remove the EGR valve and clean carbon deposits from the thermistor tip and passage using approved intake cleaner
  5. Perform a wiggle test on the wiring harness while watching live data to reveal intermittent faults
  6. If the sensor is faulty, replace the EGR valve assembly or thermistor as applicable, then clear the code and verify the repair with a road test

What most technicians overlook on P1408

  • A P1408 can be set by a perfectly functioning thermistor if the EGR passages are so carboned up that exhaust gas never reaches the sensor, so always verify flow before condemning the sensor.
  • On many Jaguar V8 engines the thermistor is not sold separately and requires replacing the entire EGR valve, which makes correct diagnosis critical to avoid unnecessary expense.
  • Intermittent wiring faults behind the engine, near the bulkhead, are a common cause that only appear when the engine is hot or during vibration; a simple resistance check at the sensor may pass.
  • The code does not always mean the EGR valve is stuck closed; a thermistor that reads too high can cause the module to command less EGR flow, leading to pinging or NOx increase without a driveability complaint.
  • After repairs, the EGR monitor may require a specific drive cycle with steady-speed cruising to run and clear the code, so a short test drive may not be enough to confirm the fix.

Can I keep driving with P1408?

You can generally continue driving with P1408 because the engine management system will default to a safe EGR strategy, but avoid long periods of heavy load or towing until the fault is repaired. If the check engine light begins flashing or you notice rough running, stop driving and seek service immediately.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Jaguar vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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