Engine Coolant Bypass Valve Control Circuit Low


This code indicates that the PCM (or one of the other supporting control modules) has detected an error in the engine coolant bypass valve control circuit. These control modules may include (but are not limited to) the transmission control module, the body control module, the antilock brake control module, the instrument panel control module, the turbo control module, the anti-theft module, the cruise control module, the traction control module, proximity alert module, and the climate control module.

Code Set Parameters

In the event of an engine coolant bypass valve control circuit error, a trouble code will be stored and a service engine soon lamp will be illuminated. Some models require multiple drive cycles (as many as eight) with a failure in order for the service engine soon lamp to be illuminated. Others models will illuminate the service engine soon lamp on the initial failure.


Symptoms may include engine overheating, decreased heater efficiency, the engine may require more time to reach normal operating temperature, a stored trouble code, and possibly an illuminated service engine soon lamp. If this code is stored and a service engine soon lamp is yet to be illuminated it may be shown as pending.

Common Causes

Unlike most other PCM codes, the most likely cause of this code being stored is a defective driver in the PCM or a poor electrical connection. Other causes may include corroded, open, or shorted wiring or connectors in the engine coolant bypass valve control circuit, a loose control module ground strap or broken ground wire, the air cleaner inlet actuator may also be defective, or the fuel control module may be faulty.

Common Misdiagnosis

Symptoms and stored codes that are present as a reaction to a communication failure are often misdiagnosed and repaired as the cause of the problem. Obviously, this leads to an unsuccessful repair. Engine misfire codes, lean exhaust codes, fuel injector codes, and virtually any other drivability or transmission code that is accompanied by a controller communication code can potentially be a pitfall for misdiagnosis. Follow the rule that says to diagnose codes in the order in which they are stored and you will improve you chances for a successful diagnosis. Utilize freeze frame data to help you determine which codes were stored first.


  • Vehicles which utilize an electronically controlled valve to remove the air (gases) from the engine coolant system are subject to present this type of code
  • The coolant degassing valve s controlled by the PCM (or other auxiliary controller) using input data from the engine coolant temperature sensor
  • Consult the vehicle service manual for the location, operating characteristics, and voltage requirements of the coolant degassing valve control circuit, connectors, and components. Other vehicle applications utilize an electronically controlled valve to cause engine coolant to bypass the radiator, engine block, heater core, or other engine cooling system components
  • The valve is controlled using a voltage signal from the PCM
  • The PCM uses input data from the engine coolant temperature sensor to calculate the operational strategy for the engine coolant bypass valve control circuit. This type of code usually represents a malfunction in the controller area network, or "CAN"
  • The CAN represents a communication bus that allows multiple microcontrollers to communicate with one another without the need for a host computer
  • It is a message based protocol originally designed for automotive use
  • The CAN bus network is actually a complex conglomeration of wiring harnesses and connectors used as a pipeline of information shared between two or more automotive control modules
  • These controllers control virtually every electrical function of the vehicle, with the PCM being the primary controller
  • Control modules receive input data from various sensors and emit output signals to system components and other control modules
  • For example: The PCM receives an input signal from the vehicle speed sensor
  • This signal is systematically forwarded to affected control modules that utilize the data to accomplish various other tasks
  • The cruise control module uses the data for speed control purposes, the traction control system uses the data to regulate vehicle traction control strategy, and the anti lock brake controller compares vehicle speed from the PCM with data inputs from individual wheel speed sensors to operate the anti lock braking system. Several tools will be instrumental in attempting to successfully diagnose this code
  • A suitable OBD-II scanner (or code reader) and a digital volt/ohmmeter will be most helpful in trying to perform a successful diagnosis
  • Begin with a visual inspection of all wiring and connectors
  • Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
  • Always retest the system after repairs are completed to ensure success. If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
  • This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
  • Continue by clearing the code and operating the vehicle to see if it returns
  • This will help to determine whether or not the malfunction is intermittent
  • After the codes are cleared, test drive the vehicle to see if the code returns
  • If the code fails to immediately return, you may have an intermittent condition
  • Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can even be attempted
  • Unlike other diagnostic codes, this type of code can sometimes be best left to a professional simply because of the bulk of circuitry involved
  • An experienced technician with a specialized scanner (Autohex or Tech II) may be able to determine the general area of the malfunction much more rapidly and easily than someone using a code reader and a digital volt ohmmeter
  • Disconnecting and testing every single pin of the CAN bus could prove to be extremely time and cost prohibitive
  • Additionally, some type of memory saving device must be installed, lest the PCM and other controllers lose their memory and require reprogramming
  • A specialized diagnostic CAN scanner will show pin values and control module operation without risking a meltdown
  • It can accurately diagnose computer and circuitry problems by monitoring vehicle operation while the vehicle is being operated
  • To diagnose this type of code using a digital volt ohmmeter would entail probing thousands of circuits, independently
  • One misplaced probe could destroy expensive control modules and require that the vehicle be totally reprogrammed. At the most, you may attempt to perform a continuity test after all control modules are disconnected, and this could literally require 40-hours or more, depending upon the vehicle
  • Some applications are equipped with up to 18 separate control modules. If you choose to tackle this monumental task, begin with a careful visual inspection of all system circuitry, connectors, and fuses
  • Control module ground circuits should be tested for continuity with battery ground
  • These types of codes are frequently caused by defective or disconnected system grounds
  • An auxiliary ground cable can be helpful in diagnosing system ground discrepancies
  • Engine and transmission ground cables, straps, and wires are sometimes left dangling after repairs are performed
  • Look for loose or corroded electrical connectors that may increase circuit resistance and cause these types of codes to be stored. Obtain a CAN bus system wiring diagram and/or pin out value chart, then use the digital volt ohmmeter to test continuity between individual controller connectors
  • Compare your findings with the manufacturer's referenced values and repair open or shorted circuits as required
  • It is often much more frugal to replace defective wiring rather than attempting to remove it from the complex web of wiring harnesses.