CAN communication Line Inspection
| Inspection Item | Inspection Condition | (+) Probe | (-) Probe | Specification | ||
|---|---|---|---|---|---|---|
| Connector | Terminal | Connector | Terminal | |||
| Resistance inspection (ECM, ICU) |
|
ECM (component side) | 77 (P-CAN high) | ECM (component side) | 60 (P-CAN low) | Approx. 120Ω |
| ICU (component side) | 17 (P-CAN high) | ICU (component side) | 18 (P-CAN low) | Approx. 120Ω | ||
| Open in circuit inspection (SRSCM ↔ OCS) |
|
SRSCM connector | 36 (P-CAN high) | OCS connector | 1 (P-CAN high) | Approx. below 1Ω |
| SRSCM connector | 35 (P-CAN low) | OCS connector | 2 (P-CAN low) | Approx. below 1Ω | ||
| C-CAN oscilloscope (OCS) |
|
OCS connector | 1 (P-CAN high) | Chassis ground | - | Fig.1 to 6 |
| OCS connector | 2 (P-CAN low) | Chassis ground | - | |||
Information
It is important to check CAN high and low at the same time to check the waveform of the CAN communication line. The CAN signal is in a bus idle state based on 2.5V (digital "1"), the high signal rises to 3.5V, the low signal falls to 1.5V, and the voltage difference between the high and low signals is "0" when 2V occurs. Is detected. In addition, it monitors whether the high and low signals have opposite voltages based on 2.5V like the waveform on the left, and monitors whether the current CAN signal is transmitted normally.
In CAN communication, a continuous "0" signal of 6 bits or more means occurrence of an error. 1 bit can be easily determined by obtaining the time when "SOF" (Start Of Frame), indicating the start of the frame, occurs. Check if the "0" signal of 6 bits or more occurs continuously during CAN communication waveform check.
- Reference voltage about 2.5V (high: 2.5V → 3.5V rise, low: 2.5V → 1.5V drop)
- Idle (2.5V) section of a certain period
- Constant data frame time
- High and low symmetrical frame shape
Good
- Fault might be intermittent and caused either by poor contact in connectors or wiring harness, or it has been repaired and control module memory is not cleared yet. Thoroughly check terminal of 12V battery, all connectors (and connections) for looseness, bending, corrosion, contamination, deterioration, and/or damage.
- Repair or replace as necessary and Go to "VERIFICATION OF REPAIR " procedure.
No Good
- Repair or replace as necessary and then, Go to "VERIFICATION OF REPAIR " procedure.