Powertrain, generic · Transmission

P0728 Engine Speed Input Circuit Intermittent

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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

Likely causes

Loose contact in signal or CAN circuit
Sensor (if fitted) dirty or loose
Intermittent crankshaft sensor fault in the engine module
Transmission module

Symptoms

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

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–300
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

engine speed signalcan bustransmission control module

Related codes

P0725P0726P0727P0718P0723

References: law.cornell.edu, gsi.ext.gm.com, saabwisonline.com.