Engine RPM Output Circuit Malfunction


The PCM has detected an abnormal voltage reading from the engine RPM output circuit. Select models require multiple ignition cycles for a service engine soon lamp to be illuminated. A code should be stored on the initial failure but may appear as a pending code until multiple failures are detected.

Code Set Parameters

If the PCM detects a voltage reading from the engine RPM output circuit that is not within a predetermined manufacturer’s reference degree, a code will be stored and a service engine soon lamp may be illuminated (see note above).


Symptoms may range from only a stored code and service engine soon illumination, to a no start condition, an inoperative tachometer, or even an erratic tachometer.

Common Causes

The most common cause of this code being stored comes from defects in system circuitry. Loose, broken, or corroded wiring and electrical connectors are common and should be investigated first. Other possible causes include a defective PCM, faulty tachometer, or bad crankshaft position/camshaft position sensor. If there are other codes related to engine RPM level or drivability stored prior to this code being stored, diagnose and repair those before attempting to diagnose this code. Freeze frame data can be useful when diagnosing this code.

Common Misdiagnosis

Technicians report that the tachometer is often replaced in error when the PCM driver is at fault.


  • The PCM uses input data from the engine to calculate and redistribute data to various control modules and components throughout the vehicle
  • Output circuits are originated in the PCM, but wiring and electrical connectors are utilized to transmit the output signals to various controller interface modules, etc. Begin your diagnosis by performing a visual inspection of PCM and engine wiring harnesses, ground wires/straps, and electrical connectors
  • Look for corrosion, damage, or disconnected wiring and/or connectors. 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. Internal control module failures are usually detected by the module in question but the CAN bus is also relevant because other control modules will likely detect the malfunction, as well
  • Individual control module failure is rare but possible
  • Follow the manufacturer’s recommended testing method for diagnosing the individual control modules and replace them as required
  • Replacement of virtually all of these control modules will require reprogramming
  • 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