PROM
PROM refers to the removable calibration chip used in the Pontiac Fiero ECM.
PROM stands for Programmable Read-Only Memory. In the Fiero ECM, the PROM contains calibration information used by the ECM to control the engine.
Overview
The PROM contains engine and vehicle-specific calibration data. This information tells the ECM how to manage fuel delivery, ignition timing, idle behavior, emissions functions, diagnostic behavior, and other engine-management functions.
The PROM must match the engine, transmission, ECM type, and vehicle configuration. An incorrect, damaged, poorly seated, or modified PROM can cause drivability problems or diagnostic trouble codes.
Location
Image wanted: Photo or diagram showing the PROM location inside the Fiero ECM. Ideally include the ECM cover removed and the PROM clearly identified.
The PROM is located inside the ECM.
Accessing it requires removing the ECM from the vehicle or opening the ECM cover, depending on the procedure being performed.
The PROM should be handled carefully. Static electricity, bent pins, corrosion, incorrect installation, or contamination can damage the PROM or cause poor contact.
Function
The ECM uses PROM calibration data to determine how the engine should be controlled.
PROM calibration data may affect:
- Fuel delivery
- Ignition timing
- Idle control
- Cold-start behavior
- Warm-up behavior
- Emissions control
- Diagnostic trouble code behavior
- Transmission-related behavior on some applications
Relationship to the ECM
The PROM works together with the ECM hardware.
The ECM is the computer itself.
The PROM contains calibration information used by that computer.
A replacement ECM may not operate correctly unless the correct PROM is installed.
Related topics:
Related trouble codes
PROM-related diagnostic trouble codes include:
- Code 51 - PROM error
Related ECM calibration or memory codes include:
Code 51
Code 51 indicates that the ECM has detected a PROM-related problem.
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 of a PROM or PROM-related problem include:
- Check engine light
- Code 51
- No-start condition
- Poor drivability
- Poor idle
- Incorrect fuel control
- Incorrect spark control
- Engine runs poorly
- Backup or limp-home behavior, depending on the failure
- Little or no obvious drivability problem in some cases
Modified PROMs
Some Fieros may have modified PROMs, especially cars with engine swaps, custom tuning, emissions changes, or previous-owner modifications.
A modified PROM may be intentional, but it can also make diagnosis more difficult if the calibration is unknown.
Related topics:
Diagnosis
Basic diagnostic checks include:
- Check for stored diagnostic trouble codes.
- Confirm whether Code 51 is present.
- Check whether the ECM has been replaced.
- Check whether the PROM has been changed or modified.
- Inspect ECM connectors.
- Inspect the PROM seating if the ECM is opened.
- Check for bent pins, corrosion, or poor contact.
- Verify that the PROM matches the engine and ECM application.
- Check power, grounds, and charging voltage if ECM-related codes are present.
- Consider ECM failure only after the PROM, connectors, power, and grounds have been checked.
Handling notes
When handling a PROM:
- Avoid static electricity.
- Do not touch contacts unnecessarily.
- Avoid bending pins.
- Install it in the correct orientation.
- Make sure it is fully seated.
- Keep it clean and dry.
- Do not force it into place.
Notes
A PROM-related code does not always mean the PROM itself is bad. Poor seating, corrosion, wrong calibration, ECM problems, power issues, or previous modifications can also cause PROM-related problems.
When replacing an ECM, the original PROM may need to be transferred to the replacement ECM if it is correct and in good condition.