OBD-I Codes List

GM 27 Quad Driver Module Second Gear Circuit Fault

Make
GM (1982-1995)
Category
Powertrain - Computer and Auxiliary Controls
Severity
Check Engine Light

How to read it

Code 27 reads as 2 flashes, pause, 7 flashes on the check-engine light. Jump terminals A and B on the ALDL connector with the key off, then turn the key on with the engine off and count the check-engine flashes.

New to flash codes? The How to Read GM OBD-I Codes with a Paperclip walks through the test and what the numbers mean. The general OBD-I guide covers the rest.

What does GM code 27 mean?

Quad Driver Module Second Gear Circuit Fault

Common causes of 27

  • Shorted second gear switch or shift solenoid circuit
  • Damaged transmission harness wiring
  • Failed quad driver output inside the ECM
  • Low transmission fluid causing erratic switch signals on some models

How to fix 27

  1. Check transmission fluid level and condition first
  2. Inspect the transmission connector for fluid intrusion and corrosion
  3. Test the second gear switch and solenoid circuits per the service manual
  4. Repair wiring faults before condemning the ECM
  5. Clear codes and road test to confirm the gear signal returns

Source

Qualified source review

Sources and review

Review: qualified. Read the source limits below.

  • GM and Chevrolet OBD1 Trouble Codes (ALDL Fault Code List)

    live reference page (troublecodes.net)

    Supports: code identity and GM meaning

    Fetched directly. Single publisher, so the record is qualified, not verified. Causes and check order are curator-written from the circuit the code names.

    https://www.troublecodes.net/gm/

Last updated 2026-09-19.

Report a correction for 27. Include your vehicle, the issue and a source if you have one.

Related Powertrain - Computer and Auxiliary Controls Codes