1
\$\begingroup\$

I've been having gearbox issues for weeks, seeming to be getting worse. Error was p0753 (gearbox solenoid A electrical) and general can bus timeouts.

Now the car will not crank, because the PATS (Passive Anti Theft System, i.e. immobiliser) is reporting can bus is down.

So using a multimeter between OBD2 pins 6 and 14 I get 60 ohms, but when I turn the key to enable electrics the resistance jumps to 165 ohms.

Does the 60 ohms mean the wiring is good, and the 165 ohms indicate that one of the can bus modules must have a fault?

\$\endgroup\$
2
  • 3
    \$\begingroup\$ Resistance cannot be measured with an active can bus as the voltage applied by the can devices will mess with your measurement. A good test to see if your measurement is being corrupted is to flip the positive and negative leads of the meter and measure again. If you get a different value (perhaps even negative!) you know that the measurement is being corrupted. \$\endgroup\$
    – Bryan
    Commented Oct 23, 2023 at 14:51
  • 1
    \$\begingroup\$ Besides that, what makes you think the OBD2 CAN bus is directly connected to the gearbox CAN bus? I don't have in-depth knowledge of how most cars design CAN internally, but from an engineering design point of view, it would be a very bad idea to mix critical control signals together with misc diagnostics on the same bus. These ought to be separate buses if the people who designed the car knew what they were doing. \$\endgroup\$
    – Lundin
    Commented Oct 23, 2023 at 15:12

1 Answer 1

Reset to default
4
\$\begingroup\$

60 ohms with no power means the wiring is good, and both terminating resistors are present.

165 ohms powered on means that you should not measure resistance on a powered circuit. The electroncs connected to the bus interferes with the operation of the resistance measurement when there are voltage or current sources as part of the circuit.

\$\endgroup\$

Not the answer you're looking for? Browse other questions tagged or ask your own question.