P1600

What Does Code P1600 Mean?

The OBD-II diagnostic trouble code P1600 signifies a “Loss of Keep Alive Memory (KAM) Power; Open Circuit.” This code is set by the Powertrain Control Module (PCM), also commonly referred to as the Engine Control Module (ECM) or Engine Control Unit (ECU), when it detects an interruption or absence of the dedicated constant battery voltage supply to its Keep Alive Memory (KAM) circuit. The KAM is a non-volatile portion of the PCM’s internal memory responsible for storing critical adaptive learning parameters that are continuously updated based on vehicle operation. These parameters include, but are not limited to, long-term fuel trims, idle air control valve positions, transmission shift strategies, and misfire detection learned values. When the PCM loses KAM power, these learned values are reset to factory default settings, requiring the module to re-learn them over subsequent drive cycles. The “Open Circuit” descriptor specifically indicates that the PCM perceives a break or discontinuity in the electrical path supplying this vital constant voltage, preventing current flow to the KAM circuit.

Common Symptoms

• Malfunction Indicator Lamp (MIL) Illumination: The “Check Engine” light will be illuminated on the dashboard.
• Rough Idle or Stalling: Due to the PCM defaulting to base fuel maps and idle strategies, potentially causing an incorrect air-fuel mixture or unstable idle speed.
• Reduced Engine Performance: The vehicle may experience hesitation, lack of power, or poor acceleration as the PCM operates on pre-programmed default values rather than optimized adaptive parameters.
• Increased Fuel Consumption: Inefficient engine operation dueating to the loss of learned fuel trims can lead to higher fuel consumption.
• Transmission Shifting Irregularities: If the PCM also controls transmission functions, erratic or harsh shifts may occur due to the loss of learned shift patterns.
• Reset Learned Parameters: Any adaptive settings stored by the PCM will be lost, potentially affecting other systems reliant on these values.

What Causes the Code P1600?

• Blown Fuse: A critical fuse dedicated to the PCM’s constant power supply (often labeled BATT, MEMORY, ECM B+, or KAM) may be blown, interrupting the voltage supply.
• Corroded or Loose Battery Terminals: Poor connection at the vehicle battery can lead to intermittent or insufficient voltage supply to sensitive electronic modules.
• Damaged Wiring Harness: An open circuit, chafed wire, or corroded connector pin within the wiring harness leading to the PCM’s constant power input can cause a complete loss of voltage.
• Faulty PCM Power Relay: While less common for the constant KAM power, a defective relay in the power distribution circuit feeding the PCM could fail to provide continuous voltage.
• Corroded or Loose PCM Connector Pins: Oxidation or poor contact at the PCM electrical connector itself can prevent proper voltage delivery to the KAM circuit.
• Internal PCM Fault: In rare instances, an internal defect within the PCM’s power supply circuit or KAM module can cause this code, even with proper external voltage supply.

How to Diagnose and Troubleshoot

Diagnosis of P1600 requires a systematic approach using a digital multimeter (DMM), an OBD-II scanner, and careful visual inspection.

1. Verify the Code and Freeze Frame Data: Connect an OBD-II scanner and confirm P1600 is present. Review freeze frame data, which captures engine parameters at the moment the code was set. This can provide clues about operational conditions when the power loss occurred.
2. Visual Inspection:
   • Inspect the vehicle battery terminals for corrosion or looseness. Clean and tighten as necessary.
   • Visually inspect the fuse boxes (under the hood and under the dash) for any blown fuses related to the PCM, ECM, MEMORY, BATT, or KAM.
   • Examine the wiring harness leading to the PCM for visible damage, chafing, cuts, or signs of rodent activity. Pay close attention to areas where the harness passes through firewalls or near sharp edges.
   • Inspect the PCM electrical connectors for signs of corrosion, bent pins, or loose connections.
3. Fuse Verification with DMM: Do not rely solely on visual inspection of fuses.
   • With the ignition OFF, use a DMM set to resistance (ohms) or continuity mode to test relevant fuses. A good fuse will show very low resistance or continuity. A blown fuse will show infinite resistance or an open circuit.
   • Alternatively, with the ignition OFF, use the DMM set to DC volts. Touch one probe to ground and the other to each test point on the top of the suspected PCM BATT/MEMORY fuse. Both sides should show battery voltage. If one side shows voltage and the other doesn’t, the fuse is blown.
4. PCM Power Supply Test (Ignition OFF):
   • Obtain a wiring diagram for the specific vehicle to identify the PCM connector pin responsible for KAM (constant battery) power.
   • Disconnect the PCM connector.
   • With the DMM set to DC volts, connect the negative lead to a known good ground (e.g., battery negative terminal).
   • Carefully probe the identified KAM power pin on the vehicle side harness connector. You should measure a voltage very close to battery voltage (e.g., 12.0-12.6V).
   • If no voltage or significantly reduced voltage is present, trace the wire back towards the fuse box to identify the open circuit. Perform continuity checks from the PCM connector pin back to the fuse box output for the KAM circuit.
5. PCM Ground Circuit Test:
   • While the PCM connector is disconnected, identify the ground pins on the vehicle-side harness connector using the wiring diagram.
   • With the DMM set to resistance (ohms), connect one lead to a known good chassis ground and the other to each ground pin on the harness connector. You should measure very low resistance (ideally < 0.5 ohms). High resistance indicates a poor ground connection.
6. Test for Voltage Drop: If voltage is present at the PCM connector but drops significantly under load, there could be high resistance in the circuit. This usually requires a loaded circuit test, which can be done by back-probing the connector with it plugged in and comparing voltage to battery.

Recommended Repairs and Solutions

Once the root cause of the P1600 code is identified through systematic diagnosis, the following repairs are typically performed:

• Replace Blown Fuses: If a blown fuse is found, replace it with a fuse of the exact same amperage rating. Investigate why the fuse blew; if it’s a recurring issue, there might be a short circuit or overload further down the line.
• Repair or Replace Wiring Harness: If an open circuit, chafed wire, or damaged connector pin is identified, repair the wiring using proper soldering techniques and heat-shrink tubing, or replace the affected section of the wiring harness. Ensure all connections are secure and corrosion-free.
• Clean and Secure Battery Terminals: If corrosion or looseness at the battery terminals was the cause, clean them thoroughly using a battery terminal brush and tighten all connections to specification. Apply anti-corrosion grease.
• Clean PCM Connector Pins: If corrosion is present on the PCM connector pins, carefully clean them using an electrical contact cleaner and a small brush. Ensure the connector is fully seated and latched.
• Replace Faulty PCM Relay: If diagnostic steps confirm a faulty relay is preventing constant power, replace the relay with a new, OEM-specified unit.
• PCM Replacement: If all external power and ground circuits to the PCM test good, and no other external faults are found, an internal fault within the PCM may be indicated. This is a last resort and should only be considered after exhaustive testing of all external circuits. PCM replacement often requires reprogramming or flashing by a dealership or specialized repair shop.

Mechanic’s Tip: After any repairs, clear the P1600 code with an OBD-II scanner. Then, perform a drive cycle that includes various driving conditions (city, highway, idle) to allow the PCM to re-learn its adaptive parameters and confirm the repair. Monitor for the code’s return. Always consult the specific vehicle’s service manual for exact wiring diagrams, fuse locations, and PCM connector pin-outs.