Diagnose ISO 15118 protocol-version mismatches between an EV and charge point using SDP and SupportedAppProtocol
domain: iso.org · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Capture the SECC Discovery Protocol (SDP) exchange first: the EV multicasts an SDP request, and the charge point's SECC responds with the TCP address/port and security option (TLS or not) the EV should connect to.
Once the TCP/TLS session is up, capture the SupportedAppProtocolReq from the EV, which lists the ISO 15118 schema versions/namespaces it supports (-2 vs -20) in priority order.
Charge point responds with SupportedAppProtocolRes selecting one mutually supported version and priority index, or a negotiation-failed status if there is no overlap.
If negotiation fails or falls back unexpectedly, check whether the charge point's firmware advertises -20 support at all — some hardware only implements -2 even though later documentation references -20 features like bidirectional power.
For bidirectional (V2X) or multi-contract Plug & Charge scenarios, confirm both sides negotiated -20 specifically before troubleshooting further up the stack, since a fallback to -2 silently removes those capabilities.
Known gotchas
A charge point and EV can both technically 'support ISO 15118' yet fail to negotiate a working session because they only share compatibility on paper — SDP/SupportedAppProtocol is where actual mutual version support is determined, and it's the first place to check, not the higher-level OCPP or vehicle logs.
ISO 15118-20 mandates TLS 1.3 while -2 environments commonly ran TLS 1.2 — a charge point upgraded to claim -20 support but still configured for TLS 1.2 will fail the security handshake in a way that looks like a version mismatch but is actually a TLS configuration gap.
Negotiation falling back to -2 silently disables -20-only features (bidirectional power, multiple Plug & Charge contracts) with no explicit error at the OCPP layer — a session can complete as a normal AC/DC charge while the intended V2X or multi-contract feature never activated.
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