JH: Tachometer Output Failure

JH: Introduction See: JH: Tachometer Output Failure - Introduction

JH1 CHECK CTO CIRCUIT FOR SHORT TO POWER IN HARNESS

• Disconnect PCM.
• Key on, engine off.
• Measure voltage of CTO circuit between PCM harness connector pin 48 and ground.

Is the voltage less than 0.5 volt?
Yes

• KEY OFF. GO to JH2

.

No

• REPAIR short circuit. VERIFY symptom no longer exists.

JH2 CHECK CTO CIRCUIT FOR SHORT TO GROUND IN HARNESS

• Disconnect instrument cluster connector.
• Measure resistance between PCM harness connector pin 48 and battery negative post.
• Measure resistance between PCM harness connector pin 48 and chassis ground.

Are both resistances greater than 10,000 ohms?
Yes

• GO to JH3

.

No

• REPAIR short circuit. VERIFY a symptom no longer exists.

JH3 CHECK CTO CIRCUIT FOR OPEN IN HARNESS

• Measure resistance between PCM harness connector pin 48 and instrument cluster harness pin.

Is the resistance less than 5.0 ohms?
Yes

• GO to JH4

.

No

• REPAIR open circuit. VERIFY symptom no longer exists.

JH4 CHECK CTO SIGNAL FROM PCM

• Reconnect PCM.
• Start engine.
• Measure voltage between CTO pin at the instrument cluster and battery negative post.

Is voltage between 3.0 and 9.0 volts?
Yes

• REFER to the Instrument Panel, Gauges and Warning Indicators.

No

• REPLACE PCM (refer to Section 2, Flash Electrically Erasable Programmable Read Only Memory (EEPROM) See: Programming and Relearning\Flash Electrically Eraseable Programmable Read Only Memory - Flash EEPROM).