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DTC codes / Chrysler codes / P1399

P1399 · ChryslerWait To Start Lamp Circuit Open Or Shorted

P1399 on a Chrysler vehicle means the engine computer has detected an open or shorted circuit in the wait-to-start lamp circuit, which is the dash indicator that tells the driver when the diesel engine's glow plugs have warmed up enough to start. The computer monitors the lamp circuit for expected voltage and current, and when the readings fall outside the normal range it stores this code and may leave the lamp inoperative or stuck on.

SystemPowertrain
Code typeChrysler specific
SeverityLow
Fix difficultyIntermediate
AreaIgnition system and misfire

Symptoms you may notice

  • The wait-to-start lamp on the instrument cluster does not illuminate at all when the key is turned to run.
  • The wait-to-start lamp stays on continuously after the engine has started and the glow plugs have cycled.
  • The engine may crank and start poorly in cold weather because the driver has no visual cue to wait for glow plug warm-up.
  • A check engine light may accompany the lamp fault on some Chrysler diesel models.
  • Often no symptoms besides the warning light, with normal starting and driving in warm weather.
  • Intermittent lamp operation that flickers or works only on some key cycles.

Common causes, most likely first

  1. Failed wait-to-start lamp bulb or light-emitting diode (LED) in the instrument cluster.
  2. Open or corroded wiring between the instrument cluster and the engine control module (ECM) or body control module (BCM).
  3. Shorted wire in the wait-to-start lamp circuit contacting ground or another circuit.
  4. Faulty glow plug control module or relay that shares the lamp signal circuit on some Chrysler diesel applications.
  5. Loose or corroded connector pins at the instrument cluster, ECM, or BCM.
  6. Internal failure in the instrument cluster circuit board affecting the lamp driver.
  7. Damaged or chafed harness section near the engine bay or under the dash.

How to diagnose and fix it

  1. Verify the wait-to-start lamp bulb or LED by removing the cluster or using a scan tool output test if the cluster supports it.
  2. Inspect the wiring harness and connectors between the cluster, ECM, and BCM for corrosion, chafing, or loose pins.
  3. Use a digital multimeter to check for open or short circuits in the wait-to-start lamp circuit with the key on and off.
  4. Check the glow plug control module and its connectors if the lamp circuit passes through it on the specific Chrysler diesel model.
  5. Perform a voltage drop test on the ground and power sides of the lamp circuit to rule out high resistance.
  6. Replace the faulty component, whether lamp, cluster, module, or harness section, after confirming the fault with meter readings.
  7. Clear the code and cycle the key several times to confirm the lamp operates correctly and the code does not return.

What the wait-to-start lamp circuit really monitors

  • The ECM often checks the lamp circuit by briefly pulsing it during key-on, so a lamp that looks fine to the eye can still set P1399 if the current draw is slightly out of range.
  • A weak or failing battery can cause this code on Chrysler diesels because low voltage during glow plug cycling makes the lamp circuit readings fall outside the expected window.
  • Technicians sometimes replace the instrument cluster when the real fault is a corroded ground behind the dash that affects the lamp driver circuit.
  • On some Chrysler diesel models the wait-to-start lamp signal passes through the glow plug control module, so a module fault can set P1399 without any problem in the cluster itself.
  • This code does not always mean the glow plugs are faulty; the lamp circuit is monitored separately from the glow plug heating circuit, and glow plug performance codes will set on their own.

Can I keep driving with P1399?

You can usually keep driving with P1399 because the fault affects only the wait-to-start indicator, not the engine's ability to run. In cold weather, wait several seconds after key-on before cranking to give the glow plugs time to heat, since the lamp may not be giving you the correct cue.

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 Chrysler vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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