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1. Vehicle
Automatic vehicle lookup — returns make, model, year, fuel, mileage, and MOT advisories
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1. Vehicle
HN06 MBF
HN06 MBF
Honda Accord 2.4 i-VTEC Executive
2006 · Petrol · Manual · Silver
Engine
2.4L i-VTEC 190 PS
Mileage
94,200 mi
MOT expires
Aug 2026
Advisories
4 noted
MOT advisories — fed into diagnosis
• Front Coil spring corroded BOTH SIDES (5.3.1 b (i))
• Rear Suspension component corroded but not seriously weakened
• Rear Subframe mounting prescribed area is corroded
• REAR REINFORCER CORRODED BADLY
Corrosion pattern noted — relevant to electrical fault diagnosis
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2. Fault Codes & Symptoms
P0685 ×
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Online mechanic communities have millions of members sharing real-world fixes. Community consensus often matches what the dealership charges £200 to diagnose.
Summary
Fault Codes
Causes
TSBs & Recalls
Community
Watch Out
P0685 ECM/PCM Power Relay Control Circuit/Open

Your 2006 Honda Accord has triggered fault code P0685, which indicates the engine control module is not receiving stable power through its relay circuit. This is an electrical fault, not an engine problem. The most common causes on this model year are corroded or loose battery connections, a faulty ECM power relay, poor ECM ground connections — particularly the G101 ground wire — or a failing ELD (Electric Load Detector) in the under-hood fuse box.

System involved
Engine Control Module (ECM) power supply circuit
Vehicle-specific notes
The 2006 Honda Accord (7th generation, 2003–2007) uses a PGM-FI Main Relay in the under-hood fuse box to supply power to the ECM. This code is set when the PGM-FI Main Relay 1 fails to properly power delivery to the ECM. Your vehicle's MOT report shows extensive corrosion throughout the suspension and subframe, which strongly suggests electrical corrosion is present in the engine bay as well.
Ranked probable causes (6)
Summary
Fault Codes
Causes
TSBs & Recalls
Community
Watch Out
Ranked probable causes
Corroded battery cable or G101 ground wire
#1 most likely
Confidence91%
Extensive corrosion on MOT + 340+ community reports confirm this as primary cause at this mileage. G101 ground point corrodes badly on 7th-gen Accords and directly interrupts ECM power supply.
Next test — cheapest first
Inspect battery terminals and the G101 ground bolt behind the battery for white/green corrosion. Clean with wire brush and battery terminal spray. Free to check — 10 minutes.
Faulty ELD (Electric Load Detector) in fuse box
#2 possible
Confidence67%
ELD failure well-documented on 7th-gen Accords. Part: 38250-SDA-A01 (~£428). Often occurs alongside ground corrosion — both should be addressed together.
Next test — cheapest first
Open under-bonnet fuse box and visually inspect ELD module for burn marks, swelling, or corrosion. If visually OK, use a multimeter to check voltage output from the ELD connector. Visual check is free.
PGM-FI Main Relay failure
#3 less likely
Confidence28%
Possible but less common at this mileage. Rule out ground corrosion first — far cheaper to test. Relay is located in the under-hood fuse box.
Next test — cheapest first
Swap the PGM-FI Main Relay 1 with an identical relay from elsewhere in the fuse box as a free test. If code clears, replace relay. Part cost ~£8–15.
Corroded or damaged engine bay wiring harness
#4 less likely
Confidence18%
Given the extensive subframe and underside corrosion noted in the MOT, moisture ingress into the engine bay wiring harness is plausible. Intermittent faults at idle are consistent with hairline breaks in corroded wires.
Next test — cheapest first
Visually inspect the main engine bay harness for chafed, cracked, or corroded sheathing — particularly near the battery and firewall. Wiggle-test individual connectors while monitoring for fault recurrence.
Poor ECM mounting point / chassis ground
#5 less likely
Confidence12%
ECM chassis ground under the passenger footwell carpet can corrode and cause intermittent power loss to the module. Less common than G101 but relevant given the corrosion pattern on this vehicle.
Next test — cheapest first
Remove the passenger footwell trim and locate the ECM ground point. Check for corrosion or looseness. Clean contact surface and re-torque. Free to inspect.
Faulty ECM/PCM (internal failure)
#6 unlikely
Confidence6%
Internal ECM failure is possible but should only be considered after all power supply and ground issues are ruled out. Community data shows ECM replacement rarely resolves P0685 alone on this model.
Next test — cheapest first
Do not replace the ECM until all ground and relay issues are confirmed resolved. If code persists after all other fixes, verify ECM supply voltage is stable with a multimeter before condemning the unit.
Summary
Fault Codes
Causes
TSBs & Recalls
Community
Watch Out
Multiple users on the same forum reported identical symptoms and confirmed the battery cable + ELD fix resolved their P0685 codes.
2003 Honda Accord LX · 4-cylinder automatic · Intermittent loss of electrical power at idle (tach and speedo drop to zero, radio cuts out, CEL triggers)
Tried but didn't fix it
Dealer software update did not resolve the issue. Code returned after clearing.
What actually fixed it
Root cause was corroded positive battery cable (part 32111-RAA-A50, £97.73) and faulty ELD/fuse box assembly (part 38250-SDA-A01, £428.70). After replacement, code cleared permanently with no recurrence.
Community agreement
95%
2004 Honda Accord EX-L · K24 4-cylinder · ~95k miles · P0685 triggered only at 60%+ throttle
Tried but didn't fix it
Initial assumption was faulty ECU (£200+ cost). Owner was hesitant to replace without confirmation.
What actually fixed it
Traced to: (1) poor ECM ground (G101 wire), (2) bad ECM power relay, (3) poor battery ground. Total parts cost £40. After 6 hours of investigation and repair, code cleared. Over 1,000 miles driven with no recurrence.
Community agreement
88%
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