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DTC codes / Subaru codes / P1560

P1560 · SubaruBack-Up Voltage Circuit Malfunction

P1560 on a Subaru means the engine control module (ECM) has detected a problem with the back-up voltage circuit that supplies memory power to the ECM when the ignition is off. The ECM monitors this circuit and sets the code when the voltage is outside the expected range, which can cause the ECM to lose learned values and stored diagnostic information.

SystemPowertrain
Code typeSubaru specific
SeverityMedium
Fix difficultyIntermediate
AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

  • Often no symptoms besides the warning light, especially if the fault is intermittent.
  • The engine may idle poorly or run rough after a battery disconnect or after the fault occurs, because the ECM has lost its learned idle and fuel trim values.
  • The check engine light may illuminate immediately after starting or after the ignition is switched off and back on.
  • In some cases, the engine may crank but not start if the ECM does not receive proper back-up power.
  • Other unrelated codes may be stored or pending because the ECM memory is not being maintained.
  • The radio or clock may lose preset memory if the same circuit feeds other memory functions, though this is less common on Subaru.

Common causes, most likely first

  1. A weak or failing car battery that cannot maintain voltage when the ignition is off.
  2. Corroded, loose, or damaged battery terminals and cables, especially the positive terminal and its fusible link connections.
  3. A blown fuse in the back-up voltage circuit, often labeled as 'back-up' or 'memory' in the under-hood fuse box.
  4. A damaged or chafed wire in the back-up voltage circuit between the battery and the ECM.
  5. Poor ground connection for the ECM or the battery, causing voltage drops on the back-up circuit.
  6. A faulty ECM that is not correctly reading the back-up voltage, though this is rare.
  7. Aftermarket accessories improperly wired into the back-up circuit, causing excessive draw or voltage drop.

How to diagnose and fix it

  1. Perform a battery test with a conductance tester and load test; replace the battery if it fails.
  2. Inspect and clean the battery terminals and cables, and check the fusible links and main fuses in the under-hood fuse box.
  3. Locate the back-up voltage fuse (often labeled 'back-up' or 'memory') and check it for continuity; replace if blown.
  4. With a digital multimeter, measure voltage at the ECM back-up voltage pin with the ignition off; it should be close to battery voltage.
  5. Check for voltage drops on both the power and ground sides of the back-up circuit while loading the circuit with a test light.
  6. Inspect the wiring harness for damage, especially near the battery and where it routes to the ECM; repair any chafed or broken wires.
  7. If all wiring and power sources are good, substitute a known-good ECM to confirm whether the ECM itself is faulty.

Back-Up Voltage Circuit Checks Most Techs Miss

  • A common mistake is to replace the ECM when the real problem is a weak battery or corroded terminal that only shows up under load; always load-test the battery and check voltage drops before condemning the module.
  • The back-up voltage circuit often shares a fuse with other memory functions, so a blown fuse may also cause the radio or clock to lose presets, which is a quick clue to check that circuit first.
  • Intermittent P1560 codes can be caused by a loose battery terminal that makes good contact most of the time but drops voltage during cranking or when the vehicle sits; wiggle-test the terminals while monitoring voltage.
  • On some Subaru models, the back-up voltage is supplied through a dedicated fuse in the engine bay fuse box that is easy to overlook because it is not labeled as an ECM fuse; consult the fuse diagram for the exact location.
  • A faulty ignition switch or relay that does not fully power down the ECM can mimic a back-up voltage fault, so verify that the ECM actually goes to sleep after the ignition is off and the key is removed.

Can I keep driving with P1560?

You can usually drive the vehicle with this code, but the ECM may lose learned values and run poorly until it relearns, and if the back-up voltage is completely lost the engine may not start. Avoid disconnecting the battery or turning off the ignition for long periods until the fault is repaired, and address the issue promptly to prevent stalling or no-start conditions.

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

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