Technical Description of OBD-II Trouble Code
No Signal in Engine Speed Input Circuit
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to all OBD-II equipped vehicles (BMW, GMC, Chevy Duramax, Saturn, Audi, Jaguar, VW, Volvo, Kia, etc.). Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
A stored code P0727 indicates that the powertrain control module (PCM) has detected no input voltage signal from the engine speed sensor. The engine speed input sensor may also be referred to as the transmission input speed sensor or the input speed sensor. A stored code P0727 can be caused by either a mechanical problem or an electrical problem.
The engine speed input sensor is typically inserted through an opening in the transmission case, near the front of the input shaft, and is fitted with a rubber O-ring (on the sensor housing) to create a seal with the transmission case. It is important to exercise caution when removing the sensor from the housing as hot transmission fluid can be harmful. Place a suitable container under the opening in the transmission to catch any fluid that may spill when the sensor is removed. Repeat this process carefully whenever you plan to remove any sensor from the transmission, regardless of whether you intend to test or replace it.
At the core of the typical engine input speed sensor circuit is a stationary mounted electromagnetic hall-effect sensor. It is mounted in such a way that a toothed reluctor ring (attached to the input shaft of the transmission) passes very closely to its magnetic tip. As the transmission input shaft rotates, the reluctor ring spins. The raised areas of the teeth on the reluctor ring are used to electromagnetically complete the engine speed input circuit, while the recessed areas between the teeth interrupt the circuit. The rapid electromagnetic completions and interruptions of the circuit create a waveform pattern. The waveform patterns represent frequency and voltage variations that the PCM recognizes as engine input speed.
A code P0727 will be stored, and a malfunction indicator lamp may illuminate, if the PCM fails to receive engine speed input signal voltage for a specific period of time and under certain circumstances. It is important to note that the transmission control module (TCM) or PCM may enter limp-in mode when this code is stored.
Related engine speed input circuit engine codes include:
Code Severity & Symptoms
A stored code P0727 should be addressed urgently as it may result in severe transmission damage and/or drivability issues.
Symptoms may include:
Causes
Possible causes for this P0727 code include:
Diagnostic and Repair Procedures
A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable vehicle information source will be necessary to accurately diagnose a stored code P0727.
Prior to diagnosing an automatic transmission related code (anything in the P0700s), it is advisable to check the condition and level of the transmission fluid.
Check the automatic transmission fluid level
Many OBD-II equipped vehicles have automatic transmission dipsticks/tubes, while others do not. Your vehicle information source will provide guidance on the proper method for checking the transmission fluid level. Inspect the transmission housing, lines, and cooler for leaks if the fluid level is low. Repair any leaks as necessary and refill the transmission according to the manufacturer’s recommendations. Ensure that no further leaks are present. Next, pay attention to the odor of the transmission fluid. If the fluid smells excessively burnt, appears extremely black, or has a heavy metallic hue, it is suspected that the transmission has experienced catastrophic mechanical failure. Once there are no more leaks and the transmission is filled with the recommended fluid, visually inspect the wiring and connectors for signs of corrosion, overheating, or other damage.
Using the Scanner
If there are no visibly damaged wiring or connectors and the transmission is filled to the recommended level with the appropriate fluid, connect the scanner to the vehicle diagnostic port and retrieve all stored codes and freeze frame data. It is recommended to write down this information as it may prove helpful during the diagnosis process.
If the P0727 code is reset, connect the scanner to the vehicle and observe the engine speed input signal (to the PCM) using the data display screen. Carefully monitor the data display screen while test driving the vehicle. Take note of the engine input speed and see if it varies significantly from the engine RPM. If it does, suspect a defective engine input speed sensor or damage/wear to the reluctor ring.
Testing the Engine Speed Input Sensor
Consult your vehicle information source and follow the testing recommendations (using the DVOM) to test the engine input speed sensor. Replace the engine input speed sensor if it does not fall within the specified range. If it is within specifications, proceed to the next step.
Testing the Engine Speed Input Sensor Circuit
Test the engine input speed sensor signal by connecting the test leads (of the DVOM) to the signal wire and the sensor ground wire at the sensor connector. Follow the manufacturer’s specifications and look for glitches/spikes in the sensor signal voltage. If the sensor signal appears to be in order, use the DVOM to test the system circuits between the sensor connector and the PCM (see note below).
Additional diagnostic notes:
