EngineLightCodes
Powertrain code

P0728 Engine Speed Input Circuit Intermittent

Severity
Fix soon
Typical repair cost
$60–$330
Do it yourself
Possible, medium
Shop time
0.5–2 hours

The transmission module needs engine speed for converter slip, shift quality and to check the turbine speed.

How the engine computer detects it

Today it almost always arrives over CAN from the engine module with a validity flag; only GM's 2007 Allison 1000 tables show a separate engine speed sensor read by the transmission module. P0728 means the engine speed signal at the transmission module drops out briefly. No manufacturer document available to us uses this code: GM's Allison 1000 detects jumps and noise of this input under P0726/P0727, and Saab's bus-based systems use those codes, too. By analogy with P0718/P0723 dropouts are counted. A loose contact in the signal or CAN circuit or an intermittent crankshaft sensor fault in the engine module is the likely cause; shifts may be harsh at times.

Written from public technical sources and not yet checked by a mechanic. How we write these pages

Symptoms

  • Occasional transmission warning lamp
  • Harsh shift now and then
  • Converter clutch releases occasionally

Common causes

  1. Loose contact in signal or CAN circuit Most likely
  2. Sensor (if fitted) dirty or loose Possible
  3. Intermittent crankshaft sensor fault in the engine module Possible
  4. Transmission module Less likely

How to diagnose P0728

  1. Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
  2. Inspect the parts involved: engine speed signal, can bus, transmission control module.
  3. Work through the causes above from most to least likely, cheapest checks first.
  4. Clear the code and drive a full drive cycle to confirm the repair held.

Reading the code

P
Powertrain
0
Generic (SAE) code
7
Transmission
28
Specific fault

Questions drivers ask

Can I drive with code P0728?

Drive gently and only as far as you need to. The engine computer may limit power to protect the engine, so avoid highways and heavy traffic until it's fixed. If the check engine light starts flashing, pull over.

Will my car pass an emissions inspection with P0728?

Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.

Can I fix P0728 myself?

Often yes, with an OBD-II scanner and basic tools. Difficulty: medium. Start with the cheapest checks before replacing expensive parts.

This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.