P0728 Engine Speed Input Circuit Intermittent Trouble Code

P0728 Engine Speed Input Circuit Intermittent

OBD-II Trouble Code Technical Description

Engine Speed Input Circuit Intermittent

What does that mean?

This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to all OBD-II equipped vehicles (Nissan, Ford, GM, Chevrolet, Dodge, Jeep, GMC, VW, Toyota, etc.). Although generic, the specific repair steps may vary depending on make/model.

If your vehicle has a stored code P0728, it means that the powertrain control module (PCM) has detected an intermittent input voltage signal from the engine speed sensor. The engine speed input sensor can sometimes be called the transmission input speed sensor or just the input speed sensor. Either a mechanical problem or an electrical problem may contribute to a stored code P0728.

 

Most engine speed input sensors are inserted through an opening in the transmission case, near the front of the input shaft. The sensor is usually fitted with a rubber O-ring (around the outside) so that it makes a seal with the opening in the transmission case. You should take care when removing the sensor from the housing as hot transmission fluid may be harmful. A suitable container should be placed under the opening in the transmission to catch any fluid that may leak once the sensor is loosened and eventually removed. You should make this a habit whenever you plan to remove any sensor from the transmission (whether you plan to test or replace it).

A stationary mounted electromagnetic hall-effect sensor is at the heart of the modern engine input speed sensor circuit. The sensor is mounted so that a toothed reluctor ring (attached to the input shaft of the transmission) passes in very close proximity to its magnetic tip, as it spins. The reluctor ring spins along with the transmission input shaft. The raised areas of the teeth on the reluctor ring electromagnetically complete the engine speed input circuit and the recessed areas between the teeth interrupt the circuit. A waveform pattern is formed by these rapid electromagnetic completions and interruptions of the circuit. The waveform patterns represent frequency and voltage fluctuations that the PCM recognizes as engine input speed.

A code P0728 will be stored, and a malfunction indicator lamp may be illuminated, if the PCM detects an intermittent or erratic signal from the engine speed input sensor for a set period of time and under certain circumstances. Keep in mind that the transmission control module (TCM) or PCM may enter limp-in mode when a P0728 is stored.

Related engine speed input circuit engine codes include:

P0725 Engine Speed input Circuit Malfunction P0726 Engine Speed Input Circuit Range/Performance P0727 Engine Speed Input Circuit No Signal

Code Severity & Symptoms

A stored code P0728 should be treated as severe due to the level of transmission damage and/or drivability issues that may result.

Symptoms may include:

Erratic or inoperative speedometer/odometer Automatic transmissions may shift harshly (limp-in mode) Transmission fails to shift or shifts erratically Inoperative or incorrect tachometer Transmission slippage or delayed engagement Additional transmission input/output speed codes may be stored

Causes

Possible causes for this P0728 code include:

Open or shorted wiring and/or connectors in the engine speed input circuit Excessive metal deposits on the magnetic tip of the sensor Defective engine speed input sensor or transmission output speed sensor Damaged or worn engine speed sensor reluctor ring Mechanical transmission failure which results in transmission/clutch slippage

Diagnostic and Repair Procedures

You will need access to a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable vehicle information source, to diagnose a stored code P0728 properly.

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