Code 51

Code 51 is a diagnostic trouble code related to the ECM PROM on the Pontiac Fiero.

Code 51 indicates that the ECM has detected a problem with the PROM, PROM installation, PROM connection, or related ECM memory function.

Overview

The PROM contains calibration information used by the ECM. This calibration tells the ECM how to control fuel, ignition, idle, emissions equipment, and other engine-management functions for a specific engine and vehicle configuration.

Code 51 is set when the ECM detects a PROM-related problem.

Flash pattern

Code 51 is displayed as:

• Five flashes
• Pause
• One flash

This represents code 51.

Animated flash pattern:

Meaning

Code 51 usually indicates a PROM error.

Possible causes include:

• PROM not seated correctly
• Wrong PROM installed
• Damaged PROM
• Corroded PROM contacts
• ECM internal problem
• Poor ECM connector contact
• Previous ECM or PROM modification
• Electrical damage to the ECM or PROM

Symptoms

Possible symptoms may include:

• Check engine light
• No-start condition
• Poor drivability
• Poor idle
• Incorrect fuel or spark behavior
• Engine runs poorly
• Engine may run in backup or limp-home behavior, depending on failure
• Little or no obvious drivability problem in some cases

Diagnosis

Basic diagnostic checks include:

1. Confirm that Code 51 is present.
2. Check whether the ECM has been replaced or modified.
3. Check whether the PROM has been changed.
4. Inspect the ECM connectors.
5. Inspect the PROM seating if the ECM is opened.
6. Check for corrosion or damaged terminals.
7. Verify that the correct PROM is installed for the engine and configuration.
8. Check for other stored trouble codes.
9. Consider ECM failure if the PROM and connections appear correct.

PROM

The PROM is a removable calibration chip inside the ECM. It should be handled carefully to avoid static damage, bent pins, contamination, or incorrect installation.

Related topics:

• PROM
• ECM
• ECM replacement
• Engine management

Modified ECMs and engine swaps

Code 51 may be relevant when an ECM has been modified, repaired, replaced, or used in an engine swap.

Related topics:

• Engine swaps
• ECM
• PCM
• PROM programming
• Custom tuning

Notes

Code 51 should be treated carefully because it relates to ECM calibration and memory. Do not replace parts randomly without checking whether the ECM and PROM are correct for the vehicle.

If the ECM has been opened recently, verify that the PROM is installed correctly and fully seated.

See also

• Diagnostic trouble codes
• ALDL diagnostics
• ECM
• PROM
• Code 52
• Code 55
• Electrical system