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DTC codes / Mercedes-Benz codes / P1615

P1615 · Mercedes-BenzIFI Control Module N37 Supply Voltage

P1615 on Mercedes-Benz vehicles indicates that the IFI control module, designated N37, has detected an out-of-range supply voltage, either too low or too high, at its power input. The module monitors its own feed and sets this code when the voltage falls outside the window required for reliable operation, which can stem from a weak battery, a failing charging system, or a wiring fault in the circuit feeding N37.

SystemPowertrain
Code typeMercedes-Benz specific
SeverityMedium
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • Illuminated check engine light or instrument cluster warning, often with no other noticeable symptoms
  • Intermittent electrical glitches such as flickering interior lights or erratic gauge behavior
  • The engine may crank slowly or fail to start if the underlying voltage problem is severe
  • Reduced function or complete shutdown of systems controlled by the IFI module, depending on the model
  • Other unrelated control modules may log low-voltage codes alongside P1615

Common causes, most likely first

  1. A weak or failing main battery that cannot maintain stable voltage under load
  2. A faulty alternator or voltage regulator causing overcharging or undercharging
  3. Corroded, loose, or damaged power and ground connections at the N37 module or its fuse box feed
  4. A blown or partially blown fuse protecting the supply circuit to the IFI control module
  5. Chafed or broken wiring in the harness between the power distribution point and N37
  6. Internal power supply fault within the IFI control module itself, though this is less common
  7. Voltage spikes or drops caused by a failing auxiliary system sharing the same circuit

How to diagnose and fix it

  1. Perform a battery load test and check the charging voltage at idle and under load to rule out the most common source
  2. Inspect and clean the battery terminals, ground straps, and the power connections at the N37 module
  3. Check the fuse and relay that supply the IFI control module circuit, replacing any that show corrosion or poor continuity
  4. Back-probe the supply voltage at the N37 connector while cranking and running to confirm whether the drop occurs at the module
  5. Perform a voltage drop test on the positive and ground sides of the circuit to locate high-resistance joints or wiring
  6. If voltage is confirmed good at the module and the code persists, test or substitute the IFI control module per Mercedes-Benz procedures
  7. Clear the code and verify repair by test-driving with a scan tool monitoring supply voltage and watching for code reset

Why P1615 Often Isn't the Module

  • A large share of P1615 cases are resolved by replacing a tired battery or cleaning a corroded ground, so the IFI module itself is rarely the culprit.
  • The code can set from a momentary voltage dip during cranking, meaning it may appear after a cold start even when the charging system tests fine afterward.
  • Mercedes-Benz models with multiple control modules sharing a power feed can set P1615 when a single poor connection upstream affects several modules at once.
  • A scan tool that only reads generic OBD-II data may not show the live supply voltage the IFI module sees, so manufacturer-level diagnostics are needed to confirm the fault.
  • Do not replace the N37 module until voltage drop testing has proven the supply circuit is sound, because a wiring fault will destroy a new module in the same way.

Can I keep driving with P1615?

You can usually drive the vehicle to a workshop if the only symptom is the warning light and the engine runs normally, but avoid long trips or heavy electrical loads until the voltage supply is checked. If the engine cranks slowly, the lights dim noticeably, or other electrical systems act erratically, stop driving and address the battery or charging system first.

Tools that help

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

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