P1602 – Engine Control Module Supply Voltage


By Reinier (Contact Me)
Last Updated 2018-10-02
Automobile Repair Shop Owner

Trouble CodeFault LocationProbable Cause
P1602 Engine Control Module Supply Voltage Low From Battery (AUDI, ISUZU, SAAB, VOLKSWAGEN)
Knock Sensor Module Performance Conditions (BUICK, CADILLAC, CHEVROLET, GMC)
Speed Control Solenoid Circuit (DODGE)
Serial Communication Problem with TCM (HYUNDAI, KIA)
Engine Control Module Immobilizer Error (MAZDA)

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What Does Code P1602 Mean?

OBD II fault code P1602 is a manufacturer specific code that is defined by carmakers Volkswagen and Audi as “Engine control module (ECM) – supply voltage low from battery”, or sometimes as “Power Supply (B+) Terminal 30 Low Voltage”, and is set when the PCM (Powertrain Control Module) detects that the battery current being supplied to the PCM when the ignition is switched off, is below a minimum allowable threshold.

Any modern PCM, also known as an ECM (Engine Control Module), is a complex computer that contains a variety of voltage regulators/stabilizers, current converters, driver circuits, and several types of memory, all of which are involved in controlling, regulating, and monitoring hundreds, if not thousands of functions in a modern vehicle.

As might be expected from a complex computer, some functions such as the OBD II fault memory, basic idling speed settings, basic ignition timing settings, and several others depend on memory functions that might be lost if the power supply to these circuits is interrupted, or  too low. In practice then, these circuits are kept powered up even when the ignition is turned off to ensure that the engine starts and runs smoothly the next time the engine is started.

On some applications, this cluster of functions is known as the KAM (Keep Alive Memory), which in some respects, is roughly analogous to the BIOS system on a PC in the sense that the BIOS system supplies the PC with basic operating instructions when it boots up. In a similar fashion, the KAM memory supplies the PCM with basic operating instructions on which to start and run until such time the PCM is able to use input data and/or feedback loops from sensors to keep the engine running.

From the above, it should be obvious that if the KAM memory is lost due to an insufficient or interrupted power supply, the basic operating instructions the PCM needs to “boot up” are not available, and the engine could be immobilized as a result. Nonetheless, when the PCM detects an insufficient power supply to the Keep Alive Memory, it will set code P1602, and may also illuminate a warning light.

Where is the P1602 sensor located?

The image above shows the PCM connector from an Audi Q7 application, with terminal 30 circled.

WARNING: It should be noted that somewhat counter intuitively, this code does NOT refer to the power supply to the actual terminal #30 as shown here, but to the various and several terminals in the connector that should have a specified current on them when the ignition is switched off. Therefore, the presence or otherwise of current on terminal #30 (as shown here) when the ignition is turned off should NOT be taken as evidence of a failure or malfunction unless the manual for the affected application explicitly states that a specified current should, or should not (as the case may be) be present on this terminal when the ignition is turned off.

What are the common causes of code P1602?

Some common causes of code P1602  could include the following-

  • Low system voltages caused by defective, damaged, or run-down batteries
  • Low system/battery voltages caused by defects in, or failures of components in the charging system, including the alternator
  • Poor battery terminal connections
  • Battery cables were removed without first installing a memory saving device to keep critical circuits powered up
  • Open circuits in the PCM/KAM power supply
  • Defective ignition switch that interrupts the power supply to the PCM when the ignition is turned off
  • Corrupted software in the Keep Alive Memory
  • Failed or failing PCM

Other Manufacturer Specific Definitions for P1602

Engine control module (ECM) to antilock brake system (ABS)/traction control system (TCS), CAN data bus -communication failure (GM)
Battery voltage monitor – malfunction (Toyota)
Engine control module (ECM) - supply voltage low from battery (Volkswagen)
Engine control module (ECM) - supply voltage low from battery (Audi)
CAN data bus -antilock brake system (ABS)/ traction control system (TCS) (Buick)
CAN data bus -antilock brake system (ABS)/ traction control system (TCS) (Cadillac)
CAN data bus -antilock brake system (ASS)/ traction control system (TCS) (Chevrolet)
Engine control module (ECM) not programmed (Chrysler)
Engine control module (ECM) not . programmed (Dodge)
Transmission control module (TCM) – serial communication problem (Hyundai)
ECM to ABS communication – circuit malfunction (Isuzu)
Engine control module (ECM) not programmed (Jeep)
Transmission control module (TCM) – communication malfunction (Kia)
Battery voltage monitor – malfunction (Lexus)
Immobilizer control module/engine control module (ECM) – communication error (Mazda)
ECM to system LSI – communication malfunction (Mitsubishi)
CAN data bus -antilock brake system (ABS)/ traction control system (TCS) (Oldsmobile)
Engine control module (ECM) not programmed (Plymouth)
CAN data bus. engine control module (ECM) toanti lock brake system (ABS)/traction control system (TCS) -signal malfunction (Pontiac)
Engine control module (ECM) – defective (Saab)
CAN data bus, antilock braking system (ASS)I traction control system (TCS) to engine control module (ECM) -lost communication (Saturn)
Engine control module (ECM) – programming error (Subaru)
Electronic throttle system (ETS), throttle return spring – malfunction (Volvo)

BAT Team Discussions for P1602

  • '03 Elantra OBD II code & M/I monitors
    [I]Please fill out the following to ask a question.[/I] [B]MAKE[/B]: Hyundai [B]MODEL[/B]: Elantra [B]YEAR[/B]: 2003 [B]MILES: 120,000 ENGINE[/B]: 2.0L [B]DESCRIBE ISSUE[/B].... The check engine light has been randomly coming on and going off for about three years on my 2003 Hyundai Elantra. This c...