This message means that the RDU asked the tachograph a question on the CAN line and got no answer at all. The RDU tries every CAN speed by itself, so no speed has to be set. The LED of the unit blinks 7 times (CAN error), see the blinking table.
If the tachograph answers but refuses the download, you get a different message: Remote downloading not enabled with service card or vehicle not under ignition.
First check: is the vehicle parked?
Many tachographs stop answering on the CAN some time after the ignition was turned off, and older ones answer only while the ignition is on. For a parked vehicle this message is normal.
The RDU Manager keeps asking the tachograph. When the vehicle is used again, the message goes away and the download starts by itself. If the vehicle downloads after it has been driven, nothing has to be done.
Start the engine and wait a few minutes:
- The message goes away: the CAN connection is fine. Right-click the vehicle in the RDU Manager and choose Check remote download to see whether this tachograph can be downloaded remotely. If you want downloads with the ignition off, ask a workshop to set the tachograph's CAN wake-up (see point 1).
- The message stays while the engine runs: go through the causes below.
Causes and what to do
1. Remote download is not switched on in the tachograph.
A workshop must switch on the CAN of the C connector and remote download on it, with its programming tool and a workshop card:
- VDO DTCO: CAN 2 on, remote download on CAN 2 enabled.
- Stoneridge SE5000: Remote Download C CAN configuration = Enable and Remote Download A CAN configuration = Disable. For downloads with the ignition off, also set Wake-up on CAN and CAN Answer Request to Both.
- Intellic EFAS: menu Installation > Remote data download = On.
After a tachograph is replaced, the new one needs these settings again.
2. The tachograph cannot be downloaded through the C connector.
Old tachographs have no remote download on the C connector, for example a Stoneridge SE5000 with software older than 7.2. A workshop can tell from the part number and the software version on the technical data printout.
If the RDU is connected to the front interface of a VDO tachograph through a K-Line converter, the front interface must first be unlocked with a DTCO Update Card Front Interface.
3. Wrong CAN resistance.
With everything connected and the ignition off, measure the resistance between pin C5 (CAN high) and pin C7 (CAN low) of the tachograph's C connector:
- About 60 ohm: correct.
- About 120 ohm: one terminator is missing. If only the RDU is connected, pins C7 and C8 must be bridged (our cable has this bridge).
- 40 ohm or less: too many terminators, usually because another unit is on the line. Remove the C7-C8 bridge.
A wrong resistance can damage the CAN interface of the tachograph or of the RDU, so measure it on every installation. Wiring drawings: RDU GPRS2 Connection Scenarios, also on the Downloads page.
4. Another unit is connected to the C connector.
A factory telematics unit, a DSRC module, a fleet management box or a second remote download unit can block the CAN. Test with only the RDU connected to the C connector. See Another unit connected to the Tachograph C port.
5. The RDU is not powered correctly.
See RDU power supply: after ignition or permanent power.
6. Damaged CAN interface.
If the resistance and the settings are right and the message stays, the CAN interface of the tachograph or of the RDU may be damaged. If a front download of the tachograph works, have a workshop check the tachograph's C connector.
Contact support
If none of this helps, open a ticket and send:
- the terminal ID,
- the tachograph make, model and software version (technical data printout),
- the measured CAN resistance, and what else is connected to the C connector,
- a photo of the wiring at the C connector,
- whether the engine was running when the message appeared.