What the app can do
The full list for the Jeep Grand Cherokee WJ/WG with the 4.7 High Output V8, every item measured on the reference car, a 2002 WG, with an Android tablet and an ELM327 adapter. Nothing here is a promise; planned work is marked as planned.
Live data
Values as they change, module by module. The engine gives the generic OBD-II set; the other modules give their own data. All of it comes over the car’s PCI bus.
Engine generic OBD-II
- Engine speed
- Vehicle speed
- Throttle position
- Calculated load
- Coolant temperature
- Intake manifold pressure
- Intake air temperature
- Ignition timing advance
- Short- and long-term fuel trims, both banks
- Upstream oxygen sensor voltages, both banks
- Monitor and check-engine lamp status
Transmission 545RFE
- Selector position: P, R, N, D, 2, 1, and the overdrive-off button
- Current gear and the last shift
- Input and output shaft speeds
- Torque-converter clutch state
- Line pressure, actual and desired
- Pressure-control duty
- Temperature state and sensor voltage
- Throttle angle as the transmission sees it
- Ignition feed and battery voltage at the controller
Worked out on top: gear ratio from the two shaft speeds, and torque-converter slip.
ABS
- Front left wheel speed
- Front right wheel speed
- Rear left wheel speed
- Rear right wheel speed
- Vehicle speed
- Brake switch
Body computer
- Each door, open or closed
- Hood, liftgate and liftgate glass
- Headlamp switch position
- Wiper switch position, including each intermittent step
- Seat-belt buckle
- Brake switch
Driver and passenger doors
- Every switch on both door panels
- Window switches
- Lock switches
- Mirror selector and direction
- Memory buttons
Memory seat
- Position sensors
- Switch inputs
Rain sensor, radio, CD changer and the alarm module answer on the bus and are identified; nothing more is claimed for them yet.
Fault codes
Stored codes are read from nine modules. Clearing is confirmed on three; on the others it is either not tried yet or deliberately left out.
9of 16| Module | Read stored codes | Clear codes |
|---|---|---|
| Engine | Yes | Not confirmed yet |
| Transmission | Yes | Confirmed |
| ABS | Yes | Not confirmed yet |
| Body computer | Yes | Not confirmed yet |
| Airbag | Yes | Never: read only |
| Instrument cluster | Yes | Confirmed |
| Overhead console | Yes | Not confirmed yet |
| Climate control | Yes | Confirmed |
| Immobiliser | Yes | Not confirmed yet |
Fifteen actuator tests
Each test makes the car do one thing on request, so you can tell a dead bulb from a bad switch. They run only while the car is standing still, and only from a fixed, reviewed list.
- Chime
- Hazard lamps
- Park lamps
- Low beam
- High beam
- Fog lamps
- Front wipers
- Rear-window defogger relay
- Alarm indicator lamp
- Door lock and unlock
- Driver window
- Passenger window
- Mirror movement
- Mirror fold
- Instrument-cluster self-test: needle sweep and lamps
Logging and tools
For looking at a drive afterwards, and for working out what went wrong when something does.
Drive log
About 120 values written to a plain CSV file while you drive. They are read in three tiers: a fast tier for values that change quickly, a rotating tier taken in turns, and a wide tier for the rest, so the quick ones stay quick.
Event marker
One button that writes a mark into the log, for “something just happened”, so the moment is easy to find later.
Session log
A live log of what the app sends and receives, for debugging the app and the adapter.
Laptop bridge
Lets a laptop use the tablet’s connection to the car, for work that is easier on a bigger screen.
Coming later
Planned, not done.
Deeper engine data
Knock retard, misfire counters and the engine computer’s other deeper data travel on a separate serial line, Chrysler’s SCI, which an ELM327 cannot speak. A dedicated interface is being looked at; when it works, these values come in. Why the engine only gives generic data.
Linux desktop app
The same core as the Android app, on a laptop.
Adapter guide
Which ELM327 clones work on this bus and which do not, written up on this site.
The app is in private testing; there is no download yet. Once it is tested and debugged, the plan is to release it as open source. Where it stands.
Module by module
Which of the sixteen modules gives live data, fault codes or tests, and what the car itself is.