P1605

What Does Code P1605 Mean?

DTC P1605, often described as “Keep Alive Memory Test Failure,” signifies that the Powertrain Control Module (PCM) or Engine Control Module (ECM) has detected an anomaly in its non-volatile memory circuit responsible for storing adaptive learning values. The Keep Alive Memory (KAM) is a dedicated segment within the PCM’s memory that retains critical learned data such as fuel trim adjustments, idle air control parameters, transmission shift adaptions, and other operational optimizations even when the ignition is switched off. This data allows the engine to operate efficiently and consistently after multiple drive cycles. The PCM performs an internal diagnostic test on the KAM circuit to ensure data integrity and continuous power supply. When this test fails, indicating either a loss of constant power to the KAM circuit, corruption of the stored data, or an internal fault within the memory hardware itself, the P1605 code is triggered. This forces the PCM to revert to its default, factory-programmed parameters, effectively losing all previously learned adaptions and potentially impacting engine performance and emissions compliance.

Common Symptoms

• Illuminated Malfunction Indicator Lamp (MIL): The “Check Engine” light will be illuminated.
• Reduced Fuel Economy: Loss of adaptive fuel trims can lead to less efficient fuel metering.
• Rough Idle or Stalling: Without learned idle control parameters, the engine may struggle to maintain a stable idle, especially after starting.
• Hesitation or Poor Throttle Response: Engine performance may feel sluggish or inconsistent as the PCM operates on generic values.
• Erratic Automatic Transmission Shifting: For vehicles with integrated powertrain control, lost transmission shift adaptions can result in harsh, delayed, or unpredictable gear changes.
• Persistent Performance Issues: The vehicle may never seem to “learn” and improve its drivability characteristics, as adaptions are constantly lost.

What Causes the Code P1605?

• Loss of Constant Battery Voltage to the PCM/ECM: This is the most prevalent cause. The KAM requires a continuous, unfused (or specifically KAM-fused) B+ power supply. An open circuit, damaged wire, corroded connector pin, or a blown fuse in this dedicated circuit will cause data loss and trigger P1605.
• Faulty PCM/ECM Internal Hardware: A failure within the PCM’s internal memory chips or associated control circuitry can prevent the KAM from retaining data or passing its self-test, even if external power is stable.
• Weak or Failing Vehicle Battery: Insufficient battery voltage, especially during cranking or prolonged periods of inactivity, can momentarily drop below the threshold required to maintain KAM data, leading to corruption or loss.
• Corrosion or Poor Electrical Connections: Corroded or loose terminals at the battery, fuse box, or the PCM/ECM connector itself can cause intermittent power loss to the KAM circuit.
• Aftermarket Accessory Interference: Improperly wired aftermarket accessories (e.g., car alarms, stereos, remote starters) that draw power from or interfere with the PCM’s constant voltage supply can inadvertently trigger this code.

How to Diagnose and Troubleshoot

Diagnosis of P1605 requires a systematic approach, focusing on electrical integrity:

1. Verify DTC and Other Codes: Connect an OBD-II scanner to confirm P1605. Note any other related codes, as they may provide clues to a broader electrical issue. Clear the code and cycle the ignition to see if it immediately returns, which would point to a hard fault.
2. Battery System Inspection:
   • Inspect the battery terminals for corrosion and ensure they are clean and tight.
   • Measure battery voltage with the engine off; it should be >12.4V.
   • Perform a battery load test to ensure it can maintain voltage under demand.
3. Identify and Inspect KAM Power Circuit:
   • Consult the vehicle’s manufacturer-specific wiring diagrams to locate the PCM/ECM’s constant battery voltage (B+) supply pin(s) for the KAM and its associated fuse(s). There may be a dedicated “memory” or “PCM B+” fuse.
   • Visually inspect the identified fuse(s) for continuity. Use a digital multimeter (DMM) to check for continuity across the fuse, as visual inspection can sometimes be misleading.
   • Inspect the fuse box and terminals for any signs of corrosion, melting, or looseness.
4. Wiring and Connector Integrity Check:
   • With the ignition OFF and the PCM/ECM connector(s) disconnected, measure voltage at the constant B+ pin(s) of the PCM harness connector to a known good chassis ground. It should read full battery voltage (~12V).
   • Perform a voltage drop test on the B+ circuit. Connect one DMM lead to the battery positive terminal and the other to the PCM’s B+ pin (with the PCM disconnected). A reading of more than 0.2V indicates excessive resistance in the circuit.
   • Measure resistance from the PCM’s B+ pin to the battery positive terminal. It should be very low, typically <0.5 ohms.
   • Similarly, identify the PCM’s ground pin(s) on the wiring diagram. Measure resistance from these pins to a known good chassis ground. It should also be <0.5 ohms.
   • Inspect the PCM/ECM connector and harness for any signs of damage, fraying, corrosion, or pushed-out pins.
5. Monitor Adaptive Values (Advanced Scanner): If the code is intermittent, use an advanced scan tool to monitor specific adaptive values (e.g., long-term fuel trims, idle air control learned values) after a drive cycle. Turn off the ignition for several minutes, then restart and recheck the values. If they have reset to default or zero, it strongly suggests a KAM power loss or internal PCM failure.

Recommended Repairs and Solutions

Addressing P1605 typically involves restoring reliable power to the PCM’s KAM circuit or, in rarer cases, replacing the module itself:

1. Replace Blown Fuses: If a blown fuse is identified, replace it with a new fuse of the exact specified amperage. Investigate why the fuse blew; a short circuit could be present elsewhere in the system.
2. Repair Wiring or Connectors: Any identified open circuits, corroded wires, or damaged connector pins in the constant power supply or ground circuits to the PCM/ECM must be meticulously repaired or replaced. Use appropriate soldering and heat-shrink methods for wire repairs.
3. Clean and Secure Battery Connections: Ensure battery terminals are thoroughly cleaned, free of corrosion, and securely tightened.
4. Replace Weak/Failing Battery: If the battery fails a load test or is consistently below optimal voltage, replacement is necessary.
5. Address Aftermarket Accessory Interference: If an aftermarket accessory is found to be improperly wired and interfering with the PCM’s constant power, it must be rewired correctly or removed.
6. PCM/ECM Replacement (Last Resort): If all external power and ground circuits to the module are verified to be robust and stable, and the P1605 code persists along with a consistent loss of learned adaptive values, the PCM/ECM itself is likely faulty. This is a significant repair that typically requires a new or re-manufactured module, often necessitating programming, coding, or immobilizer synchronization by a qualified technician using specialized tools.

Mechanic’s Tip: After performing any repairs that affect the PCM’s memory or power supply, it is often beneficial to perform a “hard reset” (disconnecting the battery for a short period, typically 10-15 minutes, after all repairs are complete) to ensure all volatile memory is cleared, forcing the PCM to start fresh with its relearning process. Follow up with a comprehensive drive cycle to allow the PCM to relearn its adaptive parameters and confirm the code does not return.