Lawmaking Fault Location Probable Crusade
P0685 ECM/PCM ability relay -circuit open up
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What Does Lawmaking P0685 Mean?

OBD II fault lawmaking P0685 is a generic code that is divers as "ECM/PCM power relay -circuit open up", and is set when the PCM (Powertrain Control Module) detects that its own power supply has failed, or if it detects a low voltage in the circuit that supplies information technology with ability. Notation that this code only applies to applications that utilise a relay to supply bombardment power to the PCM.

Most PCM power-supply circuits are relatively simple and directly forward. When the ignition is turned to the "ON" position, power is fed to the relay, which causes an electromagnet to shut two contact points- one of which is permanently connected to battery power.  When this happens, a circuit that carries battery power is completed, and battery power is so fed to the PCM via a fused circuit.

The image below shows the terminal configuration of a typical v-pin relay, such as might be institute in the PCM ability supply of many modern applications.

micro-automotive-relay-wiring

What are the common causes of lawmaking P0685 ?

Some common causes of lawmaking P0685 could include the following-

  • Defective PCM power-supply relay
  • Low system voltage
  • Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors, including battery terminals
  • Lacking ignition switch
  • Failed or failing PCM or other control module. Annotation that this is a rare event, and the fault must be sought elsewhere before any control module is replaced

What are the symptoms of code P0685 ?

Some mutual symptoms of code P0685 could include the following-

  • Stored trouble lawmaking and perhaps an illuminated alarm light
  • Note that in some cases, the CEL might be disabled or deactivated when this code is present, significant that the absence of a alert light should Not exist taken as evidence of the absence of a problem
  • In many cases, a no-start or no-crank condition will exist present
  • While the engine may offset and fifty-fifty run in some cases, the presence of code P0658 generally indicates a programming error in the PCM

How do yous troubleshoot lawmaking P0685 ?

Annotation: Most PCM relays are of the five-pin blazon. The nearly common pin configuration is given below-

  • One terminal (the primary) is permanently connected to the bombardment
  • One other terminal is also connected to the bombardment thorough contact points that are closed when the relay is energized
  • The ground final is grounded to the engine and/or chassis
  • One final is the power output that leads to the PCM
  • The remaining last is a indicate wire that connects to the Can (Controller Area Network) bus system

Pace 1

Record all error codes present, as well as all available freeze frame data. This data can be of use should an intermittent fault be diagnosed afterwards on.

Step 2

Locate the PCM power relay, but be certain to refer to the manual to determine the bodily terminal configuration, likewise as the function of each wire that connects to the relay.

WARNING: Failure to determine the function of each wire can lead to a misdiagnosis, but worse, testing the wrong wire/circuit at the wrong fourth dimension can cause short circuits that tin can have fatal consequences not but for the PCM, but also large sections of the application's electrical arrangement.

Step three

Perform a thorough visual inspection of all associated wiring, and look for burnt, shorted, disconnected, or corroded wiring and/or connectors. Make repairs equally required if damaged wiring is found.

Annotation: If blown fuses or fusible links are found, Do NOT supersede them until information technology is certain that there are no curt circuits in the circuit, or until all known short circuits have been repaired.

Pace iv

If no visible harm to wiring is plant, and there are no diddled fuses/fusible links in whatsoever associated excursion, keep to exam for voltage as per the pivot configuration given above.

WARNING: Be absolutely sure you know which excursion you going to test before actually testing it. Ever refer to the manual or wiring diagram before testing anything or any excursion to ensure that that yous non only obtain the almost authentic test results, but also to forestall inadvertently causing brusque circuits that tin destroy expensive components and/or control modules.

Step five

If a low (or no) voltage is found at either (or both) the primary and secondary terminals on the relay but all fuses/fusible links are intact, doubtable a defective ignition switch.

If the ground circuit is open, clean and retighten all grounding points. Even so, if the basis circuit shows a voltage, the circuit is shorted to bombardment positive; discover and repair the short circuit.

Cheque for organisation voltage at the PCM connector; if this voltage is low or absent, test this excursion for open circuits, or determine the reason for the low arrangement voltage. Make repairs every bit required, and retest the voltage to verify that full system voltage reaches the PCM.

Step 6

If all voltages and basis circuits check out, remove the relay and test it every bit per the instructions in the manual, paying item attention to its internal resistance, since this value is a reasonably good indicator of its overall status.

Compare all obtained readings with the values stated in the manual, and replace the relay with an OEM replacement if Whatever tested value does not agree with the stated values. Be sure withal to disconnect all relevant wiring from the PCM during resistance tests to forbid harm to the controller.

Pace vii

If all voltages and other electrical values check out, and it is sure the relay is in perfect working order, doubtable a programming fault or other defect in the PCM or other command module that shares the CAN bus network.

Notation even so that diagnosing this type of fault almost always requires the use of advanced diagnostic equipment. If a lacking control module is suspected, the better selection would be to refer the application to the dealer or other competent repair facility for professional diagnosis and repair.

Codes Related to P0685

  • P0686 – "ECM/PCM Ability Relay Command Excursion Low"
  • P0687 – "ECM/PCM Power Relay Command Circuit High"