According to Au7o's analysis of 65+ owner reports, the 2018 Peugeot 508 has 3 documented known issues, with 2 rated critical. The most serious are Diesel DPF Regeneration Issues ($300-$2,500 repair) and 1.6 THP (EP6) Timing Chain Stretch and Soft Chain Tensioner — Cold-Start Rattle ($900-$1,600 repair). Across all issues with published estimates, repair costs range from $300 to $2,500. DIY maintenance guides at au7o.io.
On the 2011-2026 Peugeot 508, the 508 diesel suffers from DPF regeneration failures, particularly on first-generation models with the additive DPF system. Frequent short journeys prevent the regeneration cycle from completing, leading to progressive soot buildup.
Perform forced DPF regeneration via diagnostic tool. Top up the Eolys additive system. For severely blocked units, professional off-car DPF cleaning is recommended before resorting to replacement.
High Confidence65 owner reportsReviewed Invalid Date
On the 2018-2022 Peugeot 508, an engine control unit software defect on BlueHDi diesel 508s stops the malfunction indicator lamp being commanded on when the AdBlue urea injector fails. The SCR system stops dosing and NOx emissions rise above the legal limit, but the driver sees nothing on the dash until the car eventually enters the AdBlue start-prevention sequence or fails an emissions check. Stellantis campaign codes MF6 and MYC cover 556,699 vehicles built 6 December 2017 to 21 November 2022 across twelve Peugeot models including the 508, and address both the urea injector MIL defect (cars built 15 June 2020 onward) and an earlier SCR/DPF diagnostic failure (cars built 6 December 2017 to 7 November 2019). This is distinct from ordinary DPF regeneration trouble — here the diagnostic itself is disabled, so the usual early warning never appears. Petrol PureTech and Hybrid 508s are not affected.
Common Symptoms
AdBlue tank level barely drops between refills
No engine warning lamp despite a dead urea injector
Fails NOx emissions testing
Later AdBlue start-prevention countdown appears without prior warning
How to Fix
Check the VIN against campaigns MF6 and MYC at a Peugeot dealer; the remedy is a free ECU software update. Ask for an SCR system inspection at the same visit — an injector that has been dead for months without a lamp often leaves urea crystallisation in the injector and dosing line, and a fouled or drifting NOx sensor, none of which the reflash fixes. Track AdBlue consumption after the update: a tank that stops draining is the practical sign the injector is still not dosing.
On the 2011-2018 Peugeot 508, the 508 I's 1.6 THP petrol is the PSA/BMW-developed EP6 'Prince' engine, whose timing chain and tensioner are a documented weak point. The root problem is not the chain itself but an over-soft hydraulic chain tensioner that bleeds off oil pressure when the engine is shut down; on the next cold start the slack chain rattles against its guides for anything from a couple of seconds to half a minute until pressure builds. Left alone, the chain elongates, valve timing drifts, the engine management logs a correlation fault and — in the worst cases — the chain jumps and destroys the valvetrain. The problem became severe enough in Europe that Austrian owners organised a collective complaint action against Peugeot Austria in 2011 over elongated timing chains in 1.6 THP engines, and forum consensus is that later production ran a revised chain and tensioner that reduced but did not eliminate the fault. Diesel HDi/BlueHDi 508s do not share this engine.
Metallic rattle from the timing end for several seconds after a cold start
Rhythmic knock from the front of the engine under load
Engine management light with camshaft/crankshaft correlation faults
Rough idle and reduced power
How to Fix
Treat a cold-start rattle as the diagnostic trigger, not a nuisance — get the chain, tensioner and guides inspected the first time it appears rather than waiting for a fault code. Replace the chain kit as a set (chain, tensioner, guides and sprockets); replacing a stretched chain while leaving the original soft tensioner is the classic repeat-failure. Keep oil changes short and use the correct low-SAPS specification, because tensioner and chain wear on this engine track directly with oil condition and stretched intervals. Budget roughly EUR 1,000-1,500 for the chain job; a quote several times that indicates consequential valvetrain damage has already occurred.
According to Au7o's analysis of 65+ owner reports, the 2018 Peugeot 508 has 3 documented issues. The most frequently reported are: Diesel DPF Regeneration Issues, 1.6 THP (EP6) Timing Chain Stretch and Soft Chain Tensioner — Cold-Start Rattle, BlueHDi AdBlue Injector Can Fail With No Dashboard Warning — Recall MF6 / MYC. Of these, 2 are rated critical and should be addressed promptly.
Is the Peugeot 508 reliable?
The 2018 Peugeot 508 has 3 known issues documented across 65+ owner reports. 2 issues are rated critical: Diesel DPF Regeneration Issues and 1.6 THP (EP6) Timing Chain Stretch and Soft Chain Tensioner — Cold-Start Rattle. Prospective buyers should inspect for these issues and factor potential repair costs into their purchase decision. Regular maintenance following the manufacturer's schedule helps prevent many common problems.
How much does it cost to fix common Peugeot 508 problems?
Repair costs for known Peugeot 508 issues range from $0 to $2,500, depending on the specific problem and whether you choose DIY or professional repair. The most critical issue, Diesel DPF Regeneration Issues, typically costs $300-$2,500 to repair. Au7o provides step-by-step DIY maintenance guides that can help reduce repair costs.
What is the 2011-2026 Peugeot 508 Diesel DPF Regeneration Issues?
The 508 diesel suffers from DPF regeneration failures, particularly on first-generation models with the additive DPF system. Frequent short journeys prevent the regeneration cycle from completing, leading to progressive soot buildup. Repairs typically run $300-$2,500. Severity: high.
What is the 2011-2018 Peugeot 508 1.6 THP (EP6) Timing Chain Stretch and Soft Chain Tensioner — Cold-Start Rattle?
The 508 I's 1.6 THP petrol is the PSA/BMW-developed EP6 'Prince' engine, whose timing chain and tensioner are a documented weak point. The root problem is not the chain itself but an over-soft hydraulic chain tensioner that bleeds off oil pressure when the engine is shut down; on… Repairs typically run $900-$1,600. Severity: high.
What is the 2018-2022 Peugeot 508 BlueHDi AdBlue Injector Can Fail With No Dashboard Warning — Recall MF6 / MYC?
An engine control unit software defect on BlueHDi diesel 508s stops the malfunction indicator lamp being commanded on when the AdBlue urea injector fails. The SCR system stops dosing and NOx emissions rise above the legal limit, but the driver sees nothing on the dash until the c… Repairs typically run $0-$0. Severity: medium.
Content on this page was compiled with AI assistance using NHTSA complaints, TSBs, owner reports, and public automotive data. While we strive for accuracy, this information may contain errors. Always verify repair procedures and specifications with your vehicle's service manual or a qualified mechanic.
