P0603 on 2017-2019 Nissan Versa Note: ECM Backup Circuit Fault Guide

What's Unique About the 2017-2019 Nissan VERSA NOTE

Nissan has specifically acknowledged this issue across many models, including the 2017-2019 Versa Note (E12), by issuing Technical Service Bulletin NTB16-018D. The bulletin explicitly states that P0603 is often the result of low battery voltage (below 11V with ignition on), a discharged battery, or battery terminal disconnections. This indicates that for this platform, the cause is far more likely to be a simple power supply issue rather than a more serious internal failure of the Engine Control Module itself. The TSB outlines a specific procedure of cycling the ignition 10 times after clearing the code to confirm the fix.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Check Engine Light is on
• Difficulty starting the engine or prolonged cranking
• Rough or unstable idle
• Hesitation or stumbling during acceleration
• Reduced fuel economy
• Engine stalling
• Transmission may shift erratically

Most Likely Causes

1. Weak or Failing Battery 🔴 High Probability → Shop Vehicle Battery As stated in Nissan TSB NTB16-018D, low battery voltage is a primary trigger for this code. If the battery voltage drops below 11V with the ignition on, the ECM can lose its Keep Alive Memory.
   How to confirm: Use a multimeter to test the battery voltage with the engine off (should be >12.4V) and while running (should be 13.5V-14.5V). A load test at an auto parts store is the most definitive way to confirm battery health.
   Typical fix: Replace the 12V vehicle battery. The common BCI group size is 51R. 🎬 Watch: Step-by-step guide to replacing your Versa battery.
   Est. part cost: $150-$250
2. Recent Battery Disconnection or Replacement 🔴 High Probability → Shop Vehicle Battery Intentionally disconnecting the battery for service, replacement, or even installing a battery disconnect switch will cut power to the ECM, causing it to lose its memory and store a P0603 code upon reconnection.
   How to confirm: Ask the vehicle owner if the battery has been disconnected or replaced recently. If so, this is the likely cause.
   Typical fix: Clear the code with an OBD-II scanner. The code should not return if the power supply is now stable. It may be necessary to perform several drive cycles to allow all readiness monitors to reset.
   Est. part cost: $0
3. Loose or Corroded Battery Terminals 🟡 Medium Probability → Shop Vehicle Battery Corrosion or loose connections create high resistance, which can cause intermittent voltage drops to the ECM, even if the battery itself is healthy. This is a common point of failure on all vehicles.
   How to confirm: Visually inspect the battery posts and cable terminals for white or greenish corrosion. Physically attempt to twist the terminals; they should not move.
   Typical fix: Disconnect the terminals (negative first), clean them and the battery posts with a wire brush, reconnect securely (positive first), and apply a terminal protector spray.
   Est. part cost: $5-$15
4. Faulty Alternator/Charging System ⚪ Low Probability → Shop Alternator If the alternator is not properly recharging the battery, the battery voltage will slowly drop during operation, eventually leading to a low voltage condition that triggers P0603.
   How to confirm: With the engine running, check the battery voltage with a multimeter. A reading below 13.2V or above 15.0V suggests a charging system problem. Most auto parts stores offer free alternator testing.
   Typical fix: Replace the alternator.
   Est. part cost: $200-$450

Rare But Worth Checking

• Blown Fuse for ECM Memory: A dedicated fuse often protects the ECM's constant power circuit. While not common to fail, it's a simple check before suspecting more complex issues. On the Versa Note, check the fuses in the panel by the driver's left knee and in the engine compartment fuse box (IPDM) near the battery.
• Faulty Engine Control Module (ECM): → Shop Engine Control Module (ECM) This is the least likely cause. All other power and ground-related possibilities should be exhausted before considering ECM replacement, as it is expensive and may require programming.
• Poor Engine or Body Ground Connection: A corroded or loose ground strap for the engine or ECM can create intermittent electrical issues, including a P0603 code.

Diagnosis Steps

1. Check if the battery has been recently disconnected or replaced. If so, clear the code and see if it returns after several drive cycles.
2. Visually inspect the battery terminals for tightness and corrosion. They should be clean and immovable by hand. Clean and tighten as necessary.
3. Using a multimeter, test the battery voltage with the engine off. It should be above 12.4 volts. A reading below 11V with the ignition on is a red flag per Nissan's TSB.
4. Start the engine and test the charging system voltage at the battery terminals. It should be between 13.5 and 14.5 volts.
5. If battery tests are inconclusive, have it professionally load-tested at an auto parts store. This is often a free service.
6. Inspect the main engine wiring harness and ground connections (battery-to-chassis, chassis-to-engine) for any signs of damage, looseness, or corrosion.
7. Check the fuse boxes for any blown fuses related to the ECM or PCM. There is one inside the cabin and one in the engine bay (IPDM). Specifically check the 15A fuse at position #50 in the IPDM.
8. If the code returns after confirming the battery and connections are good, follow the TSB procedure: clear the DTC, turn the ignition OFF, then cycle the ignition ON for 1 second and OFF for 10 seconds, repeating 10 times. If the code does not reappear as a 1st trip DTC, the issue is resolved.
9. If all the above steps do not resolve the issue, the problem may be with the ECM itself, which would require professional diagnosis.

Parts You'll Likely Need

• 12V Automotive Battery — A weak or failing battery is the most frequent cause of the voltage drop that triggers a P0603 code on this vehicle.
  Trusted brands: DieHard, Duralast, NAPA
  OEM price range: $200-$300
  Aftermarket price range: $150-$250
• Battery Terminal Cleaner and Protector Kit — Ensures a clean, solid electrical connection between the battery and the vehicle's electrical system, preventing voltage drops.
  Trusted brands: CRC, Permatex, NOCO
  Aftermarket price range: $5-$15
• Positive Battery Terminal End (OEM #24340-7F000) — If the terminal is corroded beyond cleaning or will not tighten properly, it must be replaced to ensure a solid connection.
  Trusted brands: Nissan OEM
  OEM price range: $15-$25
  Aftermarket price range: $5-$15

Technical Service Bulletins (TSBs) & Recalls

• NTB16-018D: MIL ON WITH P0603 STORED FOR ECM BACK UP CIRCUIT

Platform-Specific Known Issues

• Nissan Technical Service Bulletin NTB16-018D was issued for a wide range of Nissan vehicles, including the 2015-2019 Versa Note, for the MIL being on with DTC P0603 stored. The bulletin guides technicians to first confirm battery voltage is 11V or more, ensure terminals are clean and tight, and then erase the code. It states that repairs for a low battery condition are not a warrantable claim under the bulletin.
• The official Nissan diagnostic procedure involves clearing the code and then cycling the ignition on and off ten times to ensure the fault does not immediately return as a '1st trip DTC'.

Mechanic-Grade Diagnostic Values

• Battery Voltage (Key On, Engine Off) — expected: 11.0 volts or more. Failure: Below 11.0 volts
• Charging System Voltage (Engine at Idle) — expected: 13.5V - 14.5V. Failure: Below 13.2V or above 15.0V
• ECM Constant Power Supply (at ECM connector) — expected: Battery Voltage. Failure: 0V or significantly less than battery voltage
• Ground Circuit Voltage Drop (e.g., Battery Negative Post to Engine Block) — expected: Under 50 millivolts (0.050V). Failure: Above 50-100mV, indicating high resistance in the ground path

Hidden / Shadow Codes Worth Checking

• 1st Trip DTC: This is not a unique code number, but a status indicating a fault has been detected during the current ignition cycle. The Nissan TSB for P0603 uses this to verify a fix. If the code does not reappear as a '1st trip DTC' after the specified procedure, the fault is considered resolved. (see via Most professional OBD-II scan tools can display the fault status, distinguishing between pending, current, permanent, and 1st trip codes.)

Scan Tool Commands That Help

• Manual Procedure (No Scan Tool): IPDM E/R Self-Test Activation — To quickly verify the functionality of relays and outputs controlled by the Intelligent Power Distribution Module (IPDM), which supplies power to the ECM relay. Turn ignition ON, then press and release the driver's door jamb switch 10 times within 10 seconds, then turn ignition OFF, then ON again. The horn will chirp and tests will begin.
• Manual Procedure (Post-Repair): DTC Confirmation Procedure — After clearing P0603 to confirm the fix, as per TSB NTB16-018D. Turn ignition ON for 1 sec, then OFF for 10 sec. Repeat this cycle 10 times. If P0603 does not return as a 1st trip DTC, the repair is successful.
• Nissan CONSULT: ECM Programming / Initialization — Required when replacing the ECM with a new 'blank' unit from Nissan (e.g., part numbers starting with 23703). The tool is needed to program the vehicle's VIN and security information into the new module.

Wiring & Ground Locations

• ECM KAM Power — On related Nissan/Infiniti platforms, this is a Pink wire at Pin 93 of the main ECM harness connector.. This wire provides the constant battery voltage required to maintain the Keep Alive Memory. A fault in this specific wire or pin will directly cause P0603.
• Fuse #50 (IPDM E/R) — Located in the Intelligent Power Distribution Module (the under-hood fuse box) in the engine compartment, near the battery.. This 15-amp fuse protects the ECM's constant power supply circuit. If it blows, the KAM will lose power.
• ECM Grounds — At the ECM harness connector, pins 159 and 162 are listed as ECM grounds in wiring diagrams for the Versa.. A poor connection at these specific ground pins can prevent the ECM from functioning correctly and may trigger various codes, including P0603.
• Main Engine/Body Grounds — Key ground points are typically labeled E15 (left side of engine compartment) and E24 (right side of engine compartment). Also check for grounds under the dashboard, especially if recent work has been performed.. The ECM relies on clean chassis and engine grounds. A loose or corroded main ground strap can cause intermittent voltage issues for the entire electrical system.

Real Owner Repair Stories

• YouTube channel 'rustbucketvalleygarage' (Nissan Versa (year not specified, but similar platform)) — Check Engine Light with code P0603 after the car sat for a while.
  ❌ Tried (didn't work) The owner had proactively installed a battery disconnect switch, thinking there was a parasitic drain.
  ✅ What actually fixed it The P0603 was caused by the battery being disconnected via the switch, which erased the ECM's Keep Alive Memory. The fix was to remove the switch, ensure the battery remained connected, and clear the code with a scanner.
• YouTube channel 'Car Hospital' (Nissan Pathfinder (different model, but same code and Nissan electrical architecture)) — Check Engine Light with P0603, reduced power and acceleration.
  ❌ Tried (didn't work) Checked all fuses in the IPDM and interior fuse box., Tested various body ground points in the engine bay.
  ✅ What actually fixed it The final cause was a ground wire located under the steering column/dashboard area that had not been reconnected after a previous dashboard repair. Securing this loose ground wire and clearing the code resolved the issue.

OEM Part Supersession History

• Varies (e.g., 23703-xxxxx) → Varies — Part revision or update.
  Heads up: According to technician forums, if a replacement ECM from Nissan has a part number starting with '23703', it is a 'blank' module and requires programming with a Nissan CONSULT scan tool to function. Aftermarket suppliers may offer pre-programmed 'plug and play' units.

Model Year Variations Within This Range

• 2017-2019: The 2017 model year marked a mid-cycle refresh for the Versa Note, introducing a new 'V-Motion' grille, updated headlights, and minor interior changes like a second 12V outlet. However, the core powertrain (1.6L HR16DE) and electrical architecture relevant to diagnosing P0603 remained consistent through 2019.