I had the engine light come on and took it to the dealership. They quoted me over 8 thousand dollars to fix. I took it to a repair shop that works on luxury cars and they fixed it for less than 1000 dollars. I had to have the transducer fixed in the turbo in my engine and when they did that they found oil in the electrical harness. That was caused by the oil seperator. They told me that it was…
2018 Mercedes-Benz GLC-Class electrical problems
severe Owners of the 2018 Mercedes-Benz GLC-Class have filed 14 NHTSA complaints about the electrical at roughly $850 to repair (U.S. federal records, as of July 2026). Source: NHTSA Office of Defects Investigation. See electrical across all vehicles →
Complaints
14
Recalls
0
Avg fix
$850
| Model year | electrical complaints |
|---|---|
| 2016 GLC-Class | 12 |
| 2017 GLC-Class | 17 |
| 2018 GLC-Class (this page) | 14 |
| 2019 GLC-Class | 16 |
| 2020 GLC-Class | 10 |
| 2022 GLC-Class | 8 |
1crash
1injury
The failure pattern owners describe
Owners describe multiple classes of electrical and mechanical failures that create genuine safety hazards. The most common issue is involuntary transmission downshift: several owners report the transmission shifting from Drive to Neutral without input while on highways or city streets, causing sudden power loss and near-accidents with following vehicles. One owner experienced this five times in two months while transporting a child.
Crankcase vent system failures (code P0521) are also recurring. The crankcase separator or vent valve malfunctions, allowing oil to contaminate the engine computer and electrical harnesses. Dealers have covered the vent valve under warranty but refused to repair the resulting oil damage to computers, with quoted repair costs reaching $6,000. One repair shop fixed the underlying turbo transducer issue for under $1,000; Mercedes corporate acknowledged the defect is well-documented but refused coverage without an active fault code.
Steering wheel clock springs are breaking during normal turning, disabling all steering wheel controls and triggering airbag warnings. Backup cameras cycle off and on in Reverse despite multiple software updates. Infotainment screens display scrambled pixels during Apple CarPlay navigation. One vehicle experienced complete electrical non-start with no lights or response. Another lurched forward into a wall when parked and the brakes did not engage, deploying airbags.
Same Mercedes-Benz GLC-Class electrical reports on nearby years: 2016 · 2017 · 2019 · 2020
Failure modes owners describe
Transmission shifts to Neutral without driver input
Transmission automatically shifts from Drive to Neutral while vehicle is in motion, reducing engine power and creating hazardous traffic situations. Multiple incidents reported over weeks or months with no clear pattern.
When: Various driving conditions including highway traffic, residential streets, and during acceleration
Symptoms owners cite: Vehicle unexpectedly shifts to Neutral while driving; Loss of engine power mid-acceleration; Vehicle slows down abruptly; Multiple occurrences of same failure
Crankcase vent system malfunction (P0521)
Crankcase vent valve malfunctions or becomes blocked (code P0521E71), allowing oil to escape into the engine computer and other electrical components. Primary failure covered under warranty, but resulting oil contamination damage not covered.
When: Service visit for check engine light
Symptoms owners cite: Check engine light illuminated; Oil present on engine computer; Difficult cold starts requiring multiple cranks; Fuel smell in air conditioning output; Cannot pass vehicle inspection due to persistent check engine light
Codes mentioned: P0521, P0521E71
Repairs/costs cited: Oil separator failure caused oil to leak into electrical harness and engine computer. Repair shop quoted under $1,000; dealer quoted $6,000 for computer leak repair. Extended emissions warranty issued in 2022 but corporate refused coverage pending fault code.
Recalls/TSBs owners mention: Warranty covered crankcase vent valve replacement but not resulting oil damage to computer. Corporate refused further coverage without active fault code despite acknowledging well-documented defect.
Infotainment display scrambling during Apple CarPlay navigation
Infotainment screen displays scrambled pixels when Apple CarPlay navigation is active, rendering maps and directions unreadable while vehicle is in motion. Issue recurs after firmware update.
When: During Apple CarPlay navigation while driving
Symptoms owners cite: Scrambled pixels on infotainment screen; Map and navigation display becomes unreadable; Occurs without warning while vehicle is in motion; Problem recurs after firmware update
Repairs/costs cited: Firmware update applied January 7, 2021 at Mercedes-Benz of Indianapolis (Repair Order #624027) but did not resolve issue permanently. Dealer requesting over $250 diagnostic fee.
Recalls/TSBs owners mention: Firmware update attempted but problem recurs. No recall or Technical Service Bulletin identified by owner. Mercedes-Benz USA customer service reported unreachable.
Backup camera power cycling in Reverse
Backup camera randomly powers down and restarts when transmission is in Reverse, causing display to switch to multimedia screen. Camera also audibly cycles in/out of rear hatch during malfunction.
When: When vehicle is in Reverse
Symptoms owners cite: Backup camera display randomly cycles off and on; Screen switches to multimedia/radio/navigation; Audible clicking/popping sound from rear camera housing; Problem persists after multiple software updates
Repairs/costs cited: Multiple software updates performed per manufacturer instructions but issue continues.
Recalls/TSBs owners mention: Issue listed as recall for 2019-2021 GLC models but also present in 2018 GLC300. Manufacturer recommended software update which failed to resolve issue.
Active Brake Assist malfunction and inability to accelerate
Dashboard displays 'Active Brake Assist malfunction' warning followed immediately by vehicle losing acceleration capability. Vehicle must be shut off and restarted to restore function, triggering check engine light.
When: While driving on road
Symptoms owners cite: Active Brake Assist malfunction warning on dashboard; Vehicle will not accelerate after warning; Check engine light illuminates after restart
Repairs/costs cited: Vehicle brought to dealer five times for this issue; vehicle remained at dealer during latest report.
Steering wheel clock spring failure
Clock spring inside steering wheel breaks when turning wheel, disabling all steering wheel controls and triggering airbag light. Failure prevents horn and control pad operation.
When: During normal steering operation
Symptoms owners cite: Audible snap or wire pull felt in steering wheel during turning; All steering wheel buttons and controls become inoperable; Horn stops working; Driver side airbag light illuminates with disabled message; Passenger airbag light randomly cycles on and off; Clicking noise heard when turning steering wheel
Door locking malfunction
Vehicle doors automatically lock with keys either inside or outside the vehicle without driver input.
When: At low mileage (6,124 miles reported)
Symptoms owners cite: Doors lock automatically without driver action; Keys trapped inside or outside vehicle
Repairs/costs cited: Vehicle taken to Mercedes-Benz of Alexandria for diagnostic testing and repairs.
Recalls/TSBs owners mention: Manufacturer made aware via email.
Complete electrical non-start with no response
Vehicle fails to start with no electrical response whatsoever. Engine will not turn over, lights do not illuminate, and neither keyless nor manual ignition input produces any response.
When: After extended period of normal operation
Symptoms owners cite: Engine will not attempt to start; No lights illuminate; No response to keyless start; No response to manual key start; Complete electrical system failure
Repairs/costs cited: Mercedes-Benz roadside assistance called. Vehicle later picked up and operated normally without incidents before recurring transmission issue.
Brake failure during parking
Vehicle accelerates uncontrollably while being parked at low speed and brakes do not engage, resulting in collision with wall and airbag deployment.
When: During low-speed parking maneuver
Symptoms owners cite: Vehicle accelerates unexpectedly during parking; Brakes do not engage when applied; Collision with wall; Airbags deployed
Windshield wiper and washer system failure due to SAM unit
SAM (Selective Ampere control Module) unit failure causes windshield washer pump to fail and wiper system to malfunction. After SAM unit replacement, vehicle throws multiple codes and rear wipers become non-functional.
When: During mountain driving; wiper malfunction light came on when starting vehicle
Symptoms owners cite: Wiper malfunction light appears on startup; Front windshield wipers stop working; Back windshield wipers initially worked but failed after SAM unit replacement; Multiple fault codes appear after SAM replacement; Loss of wiper function in heavy rain creates safety hazard
Repairs/costs cited: Mechanic identified SAM unit as cause of washer pump failure. SAM unit replacement performed but created new problems with rear wipers and fault codes.
Recalls/TSBs owners mention: Dealer acknowledged faulty SAM unit and performed replacement.
No-start condition with software update codes
Vehicle fails to start with battery in good condition. Multiple fault codes present including software update code.
When: Occasion not specified in complaint
Symptoms owners cite: Vehicle will not start; Multiple fault codes present; Software update code detected
Synthesized from 14 NHTSA owner complaints — unverified consumer allegations, summarized for patterns. The verbatim filings appear below.
What owners are reporting 1 most recent
Had electrical trouble with your 2018 Mercedes-Benz GLC-Class?
File a complaint with NHTSA → It's free, official, and how every report above got here — owner filings are the federal safety record this page is built on.
Common questions
How serious is the electrical problem on the 2018 Mercedes-Benz GLC-Class?
It's a meaningful issue. 14 complaints have been filed and the failure mode causes operational problems for owners. Repairs average $850.
At what mileage does the electrical typically fail?
Based on the 14 complaints filed, electrical issues most often appear around 11,041 miles. Some report problems earlier; some make it well past 150,000 with no symptoms. Maintenance habits matter — vehicles that received timely fluid services and were not regularly overworked tend to last longer.
What does it cost to fix?
Independent shops typically charge around $850 for electrical repairs on this vehicle. Dealer pricing tends to run 20-40% higher. The exact figure depends on the specific failure mode, parts availability, and your local labor rates. If you're outside factory warranty, an extended service contract often covers this category.
Are there any recalls related to electrical?
No active recalls currently cover electrical issues on this vehicle. The complaints filed represent owner-reported failures that haven't risen to the level of a manufacturer-issued recall — but they're still worth knowing about before you buy or budget for repairs.
Related
Complaint and recall data sourced from the National Highway Traffic Safety Administration (NHTSA)
public records database. Verify the raw federal record at
nhtsa.gov/vehicle/2018/Mercedes-Benz/GLC-Class.
Severity ratings are derived from reported crashes, fires, injuries, and fatalities. Repair cost estimates are
independent-shop national averages and may differ in your area. Some links on this page are affiliate links.