Emission Control Computer ECU

Emission Control Computer (ECC) Post-Repair Troubleshooting Guide

Important: Use this guide if you reinstalled your repaired Emission Control Computer (ECC) and the problem is still happening.
Important: Please do not open/disassemble the module. Opening the module can damage it and may void warranty coverage.

This guide helps with issues like:

• Relays controlled by the ECC not working
• Solenoids controlled by the ECC not working
• Switch inputs to the ECC not working
• No communication / cannot pull data (when applicable)

Step 1: Confirm the basics before troubleshooting

• Verify the battery is fully charged and terminals are clean/tight.
• Confirm the ECC connectors are fully seated and latched.
• Inspect the ECC pins for corrosion, bent pins, or pushed-back pins.

Step 2: Key ON check (baseline behavior)

• Turn key to ON (engine OFF).
• Verify dash warning lights behave normally (no unusual flicker/resets).
• If the vehicle behaves like it has low power (dim lights, clicking relays), fix battery/grounds first.

Step 3: Check fuses that feed the ECC and related systems
Using the vehicle fuse legend, check any fuse labeled:

• ECU / ECM / ECC / EFI
• IGN / IG / ENGINE
• INJ / SOL / EGR (if equipped)
• GAUGE (sometimes powers related circuits)
  If a fuse is blown:
• Do not keep replacing it—inspect the harness/solenoid/relay it feeds for shorts or damaged wiring.

Step 4: Verify power and ground at the ECC connector
If you have a multimeter:

• With key ON, confirm the ECC has power on its main power feed(s).
• Confirm the ECC ground(s) have low resistance to chassis ground.
  If power or ground is missing or unstable:
• The ECC cannot reliably control relays/solenoids/switch logic.
• Focus on vehicle-side wiring, fuse box feeds, and ground points.

Step 5: Inspect engine-bay grounds and power connections (very common on older vehicles)

• Locate and inspect the main engine ground straps and body grounds.
• Look for rust, paint under ground lugs, loose bolts, or broken straps.
• Clean/tighten as needed, then retest.

Step 6: If relays are not working, isolate the relay vs. control issue

• Identify which relay is failing (fuel pump relay, main relay, etc.).
• Swap with a known-good relay of the same type (if applicable).
• If the relay works when swapped, replace the relay.
• If the relay still doesn’t energize, continue to Step 7.

Step 7: If solenoids are not working, isolate the solenoid vs. wiring issue

• Identify which solenoid isn’t operating (EGR, purge, etc.).
• Inspect the solenoid connector for corrosion/oil saturation.
• Check for broken wires, especially near hot/exposed engine areas.
  If the solenoid is shorted or open, it can blow fuses or prevent proper ECC control.

Step 8: Check for harness damage in the common failure zones

• Near the battery (acid damage/corrosion)
• Along the firewall (rub-through)
• Near exhaust components (heat damage)
• Around previous repairs/splices
  Any short/open in these areas can make it look like the ECC “isn’t controlling” outputs.

Step 9: Communication check (when applicable)
If your vehicle/setup supports scanning:

• Attempt to communicate with the vehicle and check for stored codes.
• If you cannot communicate:
  • Recheck ECC power/grounds and related fuses first.
  • Inspect the diagnostic connector power/ground (some vehicles won’t scan if the DLC isn’t powered).

Step 10: If the issue is intermittent

• Wiggle-test the ECC connector and nearby harness with key ON.
• If the problem changes when moving the harness:
  • Suspect a loose pin fit, broken wire inside insulation, or corrosion in a connector.

Step 11: What to send UpFix if the issue continues

• VIN (if available) and vehicle year/make/model
• Exact symptoms (which relay/solenoid/switch is not working)
• Which fuses were checked and results
• Any voltage/ground test results at the ECC connector
• Any scan tool codes or “no communication” details
• Photos of ECC connector pins and any corrosion/wiring damage found