Hey everyone! I have a 2002 Dodge CTD auto with 277k. I’m getting the “no bus” message on my odometer screen with codes 900 920 921 940 950 and 999 on the self check. The CEL, ABS, low fuel and air bag lights are on. I’ve cleaned up the connections at the PCM and fuse block, cleaned grounds and still no fix. The truck does start and drive normal so I don’t believe it’s the PCM. Any input is welcome thanks! 

Edited August 11, 20195 yr by Beam52

I’ve got the correct  voltage at the pcm lol alternator is putting out 14 volts to both batteries, ac volts is it 0.025. I honestly am very stumped right now 

Edited August 24, 20195 yr by Beam52

Would a bad sensor cause the bus to go down? I have codes p0113 p0122 p0237 and P1698 which says it is not found in the database. Also the first DTC1 is no communication with vehicle ecu

Edited August 25, 20195 yr by Beam52

1 hour ago, Beam52 said:

Would a bad sensor cause the bus to go down?

 

No. 

 

Here is the causes of the Bus Failure...

 

he CCD data bus can be monitored using the DRBIII scan tool. However, it is possible for the data bus to pass all tests since the voltage parameters will be in “range“ and false signals are being sent. There are essentially 12 “hard failures“ that can occur with the CCD data bus:

• Bus Shorted to Battery

• Bus Shorted to 5 Volts

• Bus Shorted to Ground

• Bus (+) Shorted to Bus (–)

• Bus (–) and Bus (+) Open

• Bus (+) Open

• Bus (–) Open

• No Bus Bias

• Bus Bias Level Too High

• Bus Bias Level Too Low

• No Bus Termination

• Not Receiving Bus Messages Correctly

Again you need to check the BUS+ and BUS- voltages and you should have 2.49 volts and 2.51 volts at rest after booting up and engine not running. Red probe on the Pin 11 of the OBDII port and Pin 3. The black probe goes to ground on the DVM.

 

1 hour ago, Beam52 said:

P1698 which says it is not found in the database.

 

 

I have discovered that I have no ground to the fuse box under the hood. I can put the leads on the positive post on the fuse panel and onto the negative terminal on the battery and get 12.5v but none testing the negative terminal 

There is no ground terminal in the PDC. Both of the studs are +12V from the battery. The black cable is the charge lead from the alternator. The actual PDC ground is on the front driver side fender near the headlight. 

Update: I have 2.43 and 2.45 volts to the pcm, they are the wrong voltage but it is voltage. I have -bus voltage to the ecm plug but no voltage to the +bus. I have .3 ohms from the ecm -bus to the pcm -bus and OL when the +bus wire is ohmed out.  Also when I plug the pcm in the voltage is killed. I have the abs, air bag, radio unplugged. So I’m thinking I have a short in the harness somewhere. What do y’all think? Just tested the obd connector, at first it had 1.5 volts to both -&+ bus wires, the I unplugged the timing control module and it jumped to 2.43 and 2.45v. Shorter tcm? 

Edited August 28, 20195 yr by Beam52

Well I put the truck back together today and the rpm gauge works, the abs light went off then came back on, the air bag light went off. Still have no bus, cel, intermittent abs light.