P0728: Engine Speed Input Circuit Intermittent DTC Trouble Code

In order to determine when to shift gears, the engine computer (ECU) relies on the engine input speed sensor to tell it the real-time engine speed. If the voltage signal coming from this sensor is outside of the acceptable parameters, a P0728 DTC will be stored.

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What Transmission Do I Have?

How Serious is the Code?

If the transmission can’t shift gears the way it was intended, then further damage is likely to occur.

Symptoms

Symptoms of a P0728 include:

• Check engine light
• Harsh, erratic shifts
• Transmission not able to shift gears
• Non-working speedometer
• Limp Mode
• Engine misfire/hesitation
• Engine stalls when stopped in gear

Causes

• Faulty engine speed input sensor
• Malfunctioning transmission output speed sensor
• A wiring short or other damage
• Broken, loose or corroded connectors
• Valve body or pressure related issues
• Solenoid failure

How to Diagnose the Code?

The first step that a mechanic should take when troubleshooting a P0728 DTC, is to research TSBs (Technical Service Bulletins) and software updates. The condition of the transmission fluid also needs to be evaluated, as metal fragments can prevent the magnetic sensor head from working properly. ATF leaks should be considered as a source for corroded connectors and short circuits. And frayed wires must be fixed as well. If everything appears in good order, then the engine speed input sensor will need to be tested.

Common Mistakes When Diagnosing

It’s fairly common for metal shavings or a transmission fluid leak to be the root cause of a P0728 DTC, because ATF leaking onto the wiring and connectors can lead to serious damage. And in some cases, the problem might not be the engine input speed sensor at all. Instead, it could be a fuel delivery issue, an engine misfire, or another transmission component like a faulty solenoid.

What Repairs Will Fix P0728?

• Replace engine speed input sensor
• Replace output speed sensor
• Repair or replace damaged wiring and/or connectors
• Replace solenoids
• Change transmission fluid and filter
• Fix transmission fluid leaks

Related Codes

P0720 – Output Speed Sensor Circuit Malfunction

P0721 – Output Speed Sensor Range/Performance

P0722 – Output Speed Sensor No Signal

P0723 – Output Speed Sensor Intermittent

Need a replacement transmission? Get an estimate for replacement transmissions and local installation. Look up your transmission model by vehicle make and model.

What Transmission Do I Have?

Links To Diagnostic Codes

Links To Symptoms

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