The 2020 MDX engine complaints cluster around catastrophic internal failure and electrical/fuel management problems. The largest group—spanning 15+ narratives—reports rod bearing seizure causing engine knock that escalates to sudden loss of power on highways or city streets. Owners describe knocking sounds starting light and becoming loud within days or weeks, followed by metal shavings in the oil and complete engine failure requiring replacement ($9K–$25K). Many of these failures occur after dealership recalls for connecting rod bearing defects (NHTSA 23V-751), suggesting either incomplete repair or additional wear post-service.
A second major failure mode is auto idle stop malfunction: the engine shuts off at red lights without restarting for up to a minute, forcing drivers to power-cycle the vehicle while traffic builds behind them. This happens across multiple visits to dealers, persists after software updates and battery replacement, and creates real collision risk in busy intersections. Acura issued a service bulletin acknowledging the problem in January 2023, but no formal recall covers 2020 models.
A third group reports complete loss of motive power while driving at highway speeds—the engine simply stops with no warning light or symptom, leaving drivers coasting across traffic lanes. Some vehicles restart after multiple attempts; others require towing. Dealers consistently report inability to diagnose these issues when the engine runs fine during inspection, and NHTSA recall work hasn't resolved them for many owners.
Failure modes owners describe
Rod bearing and internal engine seizure
Catastrophic internal engine failure involving spun rod bearings, seized crankshaft bearings, excessive metal debris in oil pan, and damage to internal engine components (cam, rockers, tensioner). Owners report knocking sounds progressing to complete loss of power and engine stalling.
When: Typically 86,000–105,000 miles; one reported at 63,744 miles
Symptoms owners cite: Engine knock, initially light then becoming loud; Worsening knock when engine revs above 2000 RPM or during acceleration; Grinding noise on cold start; Loss of engine power without warning; Check engine light flashing; Excessive metal shavings in oil pan; Engine seizure/complete shutdown
Codes mentioned: P0011 (cam timing issues, inferred from owner-reported bad cam/rockers/tensioner), Misfire codes (reported in narrative #30)
Repairs/costs cited: Engine replacement required; quoted $9,000–$25,000 new engine, $8,747 used engine. Some owners claim dealer initially misdiagnosed as camshaft/rocker/tensioner issue at $3,606, though independent mechanics confirmed full engine replacement necessary. One owner claims recall service performed March 2024 may have caused subsequent failure.
Recalls/TSBs owners mention: NHTSA Recall 23V-751 and Service Bulletin 24-001 issued for connecting rod bearing defect; however, many affected VINs reported not included in recall population despite matching failure symptoms. Acura initially unwilling to cover costs even on recalled vehicles; partial coverage reported after customer documentation.
Auto idle stop malfunction (unintended stall/restart failure)
Auto idle stop feature engages at red lights and causes engine to shut off; vehicle then fails to restart immediately or at all, forcing drivers to shift to Park and manually restart. Occurs without warning and persists across multiple dealer visits and software updates.
When: Intermittent; reported at 25,000–101,000 miles; no clear mileage pattern
Symptoms owners cite: Engine shuts off at red lights or stop signs when idle stop engages; Vehicle shifts unexpectedly into Neutral without driver input; Restart failure or severe delay (up to 1 minute reported); Dashboard lights flashing; Vehicle Stability Assist Code U3006-16 appears on infotainment; No warning prior to failure; Cannot be permanently disabled by driver
Codes mentioned: U3006-16 (Vehicle Stability Assist Code)
Repairs/costs cited: Battery replacement attempted (failed to resolve); software update performed (failed to resolve). Dealers report inability to replicate issue. No successful repair documented in narratives.
Recalls/TSBs owners mention: Service Bulletin issued January 2023 acknowledging issue and showing resolution path, but no formal recall issued for 2020 MDX. One owner reports recall exists for 2022–2025 models only. Acura service personnel state issue exists but cannot fix it during visits.
Intermittent loss of motive power while driving
Vehicle loses all engine power or propulsion without warning while in motion at various speeds (highway passing, normal city driving, 55–70 mph). Engine stalls and either restarts after multiple attempts or requires towing.
When: Multiple incidents reported 4–12 months prior to complaints; mileage range 36,000–101,000 miles
Symptoms owners cite: Complete loss of power/acceleration; Engine stalls mid-drive; Check engine light flashing; Abnormal knocking sound from engine compartment; Vehicle cannot accelerate even with throttle depressed; No warning prior to failure
Codes mentioned: Check engine light (flashing), Misfire codes (inferred from symptoms)
Repairs/costs cited: Multiple owners suspect rod bearing failure but dealers unable to diagnose without engine tear-down or restart before codes clear. One owner towed; no final diagnosis/repair documented. Owners left stranded on highways and interstates.
Recalls/TSBs owners mention: Related to NHTSA Campaign 23V-751 and RQ24013 investigation per owner statements, but VINs frequently not included in recall despite matching symptoms.
Transmission shift malfunction (neutral lock-up)
Transmission unexpectedly shifts into Neutral or engages Neutral without driver command at stop lights; vehicle will not shift back into Drive and displays 'Shift to Park' message on display. Requires engine off/on cycle to resolve.
When: Intermittent, occurring at traffic lights; reported at 31,000–101,000 miles
Symptoms owners cite: Vehicle shifts to Neutral at red lights without driver input; Cannot shift back to Drive; 'Shift to Park' message on dash; Transmission stuck in Neutral; Happens 1–3 times (recurring in some cases); No warning prior to failure
Repairs/costs cited: Requires engine power-off and restart; manual locking/unlocking of doors may be required. Dealer attributed to battery issue and replaced battery; problem recurred. One narrative suggests downshift feature malfunction may be related.
Recalls/TSBs owners mention: Dealers claim no knowledge of issue; battery replacement attempted without success.
Engine noise (rod knock/clanking)
Audible knocking, clanking, ticking, or grinding sound from engine compartment, particularly on cold start or under acceleration. Sound worsens with RPM and correlates with internal bearing wear or rod failure.
When: Mileage range 55,000–101,000 miles; often develops progressively over weeks
Symptoms owners cite: Light knock on cold starts progressing to loud knock under load; Clanking noise from engine bay; Grinding noise on engine start; Ticking noise while idling; Sound worsens above 2000 RPM; Noise similar to failing crankshaft per experienced mechanic assessment
Repairs/costs cited: Dealers unable to locate source during multiple visits. Mobile mechanics and independent Honda-certified techs advise internal engine inspection; no parts available for repair short of engine replacement.
Recalls/TSBs owners mention: Dealers report issue may be 'normal' (one case); others defer diagnosis pending detailed inspection.
Hard start / delayed start
Vehicle hesitates to start or fails to start on first attempt; requires multiple key turns or extended crank time. Occurs intermittently, often after recall work or unrelated to battery condition.
When: Reported at 25,000–32,000 miles; timing varies
Symptoms owners cite: Engine hesitates to start; Multiple restart attempts required; Difficult to turn over; Occurs after recall service in some cases; No warning light
Repairs/costs cited: Battery replacement unsuccessful in one case. Dealers note battery is in good condition; unable to diagnose root cause.
Recalls/TSBs owners mention: Recall (23V-751, 23V-858) parts unavailable, delaying diagnosis.
Synthesized from 60 NHTSA owner complaints — unverified consumer
allegations, summarized for patterns. The verbatim filings appear below.