Editing CAN bus Mapping

__TOC__

== Introduction ==

This page documents CAN bus signals and decoding investigations on the Lotus Exige V6 platform. The reference vehicle is a '''2021 Lotus Exige 390 Final Edition'''. Some signals may be shared with other Exige, Evora or Elise models, but such compatibility should not be assumed without testing.

The work uses a passive, '''listen-only''' CAN interface to collect standard 11-bit CAN frames from the high-speed vehicle bus. No control or diagnostic frames are intentionally transmitted. The purpose is to support data logging and an iPhone dashboard without altering the vehicle.

'''Last updated: 19 October 2026.'''

For discussion, evidence and contributions, see the [https://forums.seloc.org/viewthread.php?tid=510758 SELOC CAN Bus Mapping thread].

=== Evidence classifications ===

* '''Confirmed''' – Signal behaviour identified through tests on the reference car.
* '''Identified in firmware''' – Working application-level interpretation; exact underlying raw mapping not yet published here.
* '''Provisional''' – Candidate byte, scaling or interpretation requiring additional correlation.
* '''Reference''' – From an earlier third-party mapping, not yet independently validated on this car.
* '''Observed''' – Frame captured but meaning unknown.

Unless specified otherwise, all byte indexes are '''zero-based''' (B0 is the first byte); all identifiers and masks are hexadecimal.

== Test vehicle and equipment ==

{| class="wikitable"
! Item !! Detail
|-
| Vehicle || 2021 Lotus Exige 390 Final Edition, 3.5-litre V6
|-
| Network || High-speed CAN, 500 kbit/s, standard 11-bit frames
|-
| OBD-II connection || Pin 6 (CAN-H), pin 14 (CAN-L)
|-
| Microcontroller || ESP32-C3
|-
| Transceiver || SN65HVD230
|-
| Interface mode || CAN listen-only (passive capture)
|-
| Output || BLE connection to iPhone dashboard
|}

The CAN reader is not an OBD-II PID scanner: it listens to native broadcast CAN messages. Generic OBD-II diagnostic requests and responses are a separate mechanism; see [[On board diagnostics]].

'''Safety:''' Do not add unnecessary bus termination. 

== CAN identifier summary ==

{| class="wikitable sortable"
! CAN ID !! DLC !! Candidate or decoded function !! Status
|-
| <code>0x085</code> || 5 || Steering angle || '''Confirmed'''
|-
| <code>0x0A2</code> || 7 || Wheel speed / vehicle speed || Reference
|-
| <code>0x0A4</code> || 8 || Additional wheel speeds || Reference
|-
| <code>0x0A8</code> || 3 || Mode/status candidate || Provisional
|-
| <code>0x102</code> || 3 || Unknown frame || Observed
|-
| <code>0x114</code> || 6 || Throttle, clutch, brake, mode button; RPM reference || Mixed (see below)
|-
| <code>0x0B7</code> || 7 || Unknown high-rate frame || Observed
|-
| <code>0x303</code> || 7 || Chassis dynamics (yaw / lateral acceleration) || Provisional
|-
| <code>0x400</code> || 7 || Vehicle status; fuel and temperature hypotheses || Observed / provisional
|}

'''Driving mode:''' Normal, Sport and Race are identified and displayed correctly by the project firmware and iPhone app. The exact raw source CAN byte or state-machine definition is not yet documented on this page; do not equate the mode-button bit with a direct selected-mode byte.

== Detailed CAN mappings ==

=== 0x085 – Steering angle ===

'''DLC:''' 5

{| class="wikitable"
! Bytes !! Encoding !! Formula !! Status
|-
| B0–B1 || Signed 16-bit, little-endian || Steering angle (degrees) = raw × 0.09 || '''Confirmed'''
|-
| B2–B4 || Undetermined || – || Unknown
|}

=== 0x0A2 – Wheel/vehicle speed ===

'''DLC:''' 7. An earlier Exige V6 RaceCapturePRO mapping associates this identifier with wheel/vehicle speed. Byte-level decoding has not yet been confirmed on this reference vehicle.

'''Status: Reference.'''

=== 0x0A4 – Additional wheel speed ===

'''DLC:''' 8. Earlier RaceCapturePRO material identifies additional wheel-speed information here. Byte-level validation remains outstanding.

'''Status: Reference.'''

=== 0x0A8 – Candidate status ===

'''DLC:''' 3

{| class="wikitable"
! Byte !! Observations !! Interpretation !! Status
|-
| B1 || <code>0x01</code>, <code>0x09</code> || Possible vehicle or mode status; not conclusively decoded || Provisional
|}

Do not treat these raw values as an established Normal/Sport/Race mapping.

=== 0x102 – Unidentified frame ===

'''DLC:''' 3. Example at standstill: <code>00 00 9C</code>. '''Status: Observed.'''

=== 0x114 – Engine and driver inputs ===

'''DLC:''' 6

{| class="wikitable"
! Byte/bit !! Signal !! Decode !! Status
|-
| B0–B1 || Engine RPM || Older reference: 16-bit raw × 0.25; endian/order must be checked against captures || Reference / calibration tested
|-
| B3 || Throttle / accelerator || Percent = raw × 100 / 255 || '''Confirmed'''
|-
| B4 bits 4–5 (<code>0x30</code>) || Clutch input || See below || '''Confirmed'''
|-
| B4 bit 7 (<code>0x80</code>) || Drive-mode button activity || 0 = inactive; 1 = active || '''Confirmed'''
|-
| B5 bit 0 (<code>0x01</code>) || Brake pedal || 0 = released; 1 = pressed || '''Confirmed'''
|}

==== Clutch input ====

Apply mask <code>0x30</code> to B4:

{| class="wikitable"
! Masked value !! Observed state
|-
| <code>0x00</code> || Released
|-
| <code>0x10</code> || Intermediate
|-
| <code>0x20</code> || Deeper / fully pressed
|}

==== Drive-mode button versus selected mode ====

B4 bit 7 captures activity of the mode selector. It does '''not''' directly report the selected driving mode. See [[#Driving modes – Normal, Sport and Race|Driving modes]].

==== Engine RPM testing ====

Engine tests have included idle and approximate 2,000 and 3,000 RPM holds. A discrepancy between the dashboard and an initial iPhone display led to subsequent firmware corrections. Publish a final byte order and scaling only after checking the corrected output against recorded raw frames.

=== 0x0B7 – High-rate unidentified frame ===

'''DLC:''' 7. B3 and B6 change frequently. '''Status: Observed.'''

=== 0x303 – Vehicle dynamics ===

'''DLC:''' 7. A strong candidate for yaw-rate and lateral-acceleration data. B4 has been investigated for lateral acceleration, but signedness, offsets and scale factors are not yet validated.

'''Status: Provisional.'''

=== 0x400 – Vehicle status, coolant and fuel candidates ===

'''DLC:''' 7

Recorded example: <code>00 00 00 02 C4 81 18</code>

The following assignments were investigated during firmware development and are '''not yet a validated decoding of this entire frame''':

{| class="wikitable"
! Byte !! Candidate signal !! Proposed calculation !! Status
|-
| B4 || Fuel level || Percent = raw × 100 / 255 || Provisional; exact byte/source needs correlation
|-
| B6 || Coolant temperature || Degrees C = raw − 40 || Provisional; raw frame correlation required
|}

'''Consistency check:''' In the example frame B6 is hexadecimal <code>0x18</code> (decimal 24), giving −16°C under the proposed temperature formula. That is not a plausible warm-engine reading. Accordingly, the example does '''not''' validate this coolant mapping. Similarly, B4 is <code>0xC4</code> (decimal 196), not the separately observed fuel candidate raw value 137. Avoid combining measurements taken at different times into a single supposedly validated frame.

== Driving modes – Normal, Sport and Race ==

'''Status: Identified and working in firmware / iPhone application.'''

The three selected drive modes have been identified in project testing. The firmware distinguishes the states and passes the result to the iPhone display.

{| class="wikitable"
! Decoded state !! Displayed mode !! Project status
|-
| 0 || Normal || Identified
|-
| 1 || Sport || Identified
|-
| 2 || Race || Identified
|}

These values are '''decoded application states'''. They are not presented as raw values from a specific CAN byte until the underlying message, byte/bit and test captures are documented here.

'''Related known signal:''' <code>0x114</code>, B4 bit 7 (<code>0x80</code>) = drive-mode button input. This is separate from the selected-mode value.

== Coolant temperature – test record ==

Dashboard readings from one stationary warm-up/cool-down test:

{| class="wikitable sortable"
! Time !! Dashboard temperature !! Condition
|-
| 19:09 || 46°C || Engine running
|-
| 19:14 || 68°C || Engine running
|-
| 19:17 || 78°C || Engine running
|-
| 19:19 || 84°C || Engine running
|-
| 19:21 || 84°C || Engine stopped; ignition on
|-
| 19:39 || 68°C || Engine off; ignition switched off after observation
|}

The dashboard trace is a useful ground-truth comparison for raw CAN captures. A conventional <code>raw − 40</code> temperature decoding has been investigated. '''A definitive ID/byte assignment cannot be claimed solely from these dashboard observations.'''

== Fuel-level candidate ==

A provisional fuel-level calculation is:

<code>Fuel (%) = raw × 100 / 255</code>

For an observed raw value of 137, the calculated level is <code>53.7%</code>, broadly consistent with a dashboard gauge near half full. This is an initial plausibility check only, not proof of the byte assignment or a linear relationship over the entire tank range. Further measurements while refuelling and driving are needed.

== Calculated gear position ==

The Exige uses a manual gearbox. A gear estimate can be derived by comparing engine RPM with vehicle speed and matching the RPM/speed ratio against expected ratios for each gear. Neutral, clutch operation, low speed and wheel slip require special handling.

'''Status: Algorithm tested successfully with simulated inputs on the bench; in-car driving validation outstanding.'''

== iPhone display project ==

An ESP32-C3 sends decoded data over BLE to an iPhone application. The iPhone app was at '''version 1.1''' during this work; the ESP32 firmware has an independent version history.

{| class="wikitable"
! Information !! Status
|-
| Steering angle || Confirmed CAN signal
|-
| Accelerator input || Confirmed CAN signal
|-
| Clutch and brake switches || Confirmed CAN signals
|-
| Normal / Sport / Race mode || Identified and displayed by app
|-
| Engine RPM || Display/calibration tested
|-
| Coolant temperature || Temperature observations recorded; byte map provisional
|-
| Fuel level || Provisional decoding
|-
| Vehicle speed / wheel speeds || Reference mapping, road validation pending
|-
| Calculated gear || Bench tested, road validation pending
|-
| Yaw/lateral acceleration || Candidate signal
|-
| Exhaust valve state || Not yet identified
|-
| TPMS values || Not yet identified on the CAN bus
|}

== Open investigations ==

* Publish raw CAN evidence and exact byte/bit decoding for the '''selected driving-mode state''' (modes themselves have been identified).
* Confirm coolant-temperature CAN ID, byte and scaling against dashboard reference values.
* Confirm fuel-level source, scaling and tank-gauge behaviour.
* Validate wheel speeds and calculated gear while driving.
* Validate yaw rate and lateral acceleration, including scale and sign.
* Investigate exhaust-valve state and whether TPMS information is broadcast on the accessible bus.
* Check mappings on other Lotus models and model years.

== Contributing a new mapping ==

Please include the vehicle model/year, CAN ID, DLC, zero-based byte/bit, raw sample frame(s), interpretation, formula, units, capture/test conditions and whether the finding was independently confirmed. Avoid marking a value as confirmed based on a single static frame or a coincidental numerical match.

{| class="wikitable"
! Field !! Example
|-
| Vehicle || Exige 390 FE, 2021
|-
| CAN ID || <code>0x085</code>
|-
| DLC || 5
|-
| Data location || B0–B1
|-
| Data type || Signed 16-bit, little-endian
|-
| Conversion || raw × 0.09°
|-
| Test || Turn steering wheel and compare observed changes
|-
| Status || Confirmed
|}

== References and further reading ==

* [https://forums.seloc.org/viewthread.php?tid=510758 SELOC forums – CAN Bus Mapping Thread] – ongoing testing and discussion.
* [https://forums.thelotusforums.com/topic/83886-exige-v6-can-bus-mapping-for-racecapturepro/ The Lotus Forums – Exige V6 CAN bus mapping for RaceCapturePRO] – earlier reference definitions.
* [[On board diagnostics]] – SELOC TechWiki background on diagnostic connectors and CAN.

== Disclaimer ==

This is independent enthusiast reverse engineering, not an official Lotus specification. Differences may exist between ECUs, model years, variants and firmware. Provisional definitions should not be relied upon for safety-critical uses or used to control vehicle functions.

[[Category:Electrical]]
[[Category:Lotus Evora]]