2nd Gen Non-Engine/Transmission Central Timer Module

[bnbrown]

I am trying to diagnose a "no bus" issue, anyone know what all the CTM runs? I thought I read somewhere the ctm is the source for the 5v bus, also if a unit can be swapped from one truck to another?

 

[Road Dog]

My 2001 FSM states there are three versions of the CTM (base, highline & premium). While it connects to the data bus I doubt it has anything to do with your "no bus" message.



Skipping pages of tedious diagnostics and airbag warnings:



The instrument cluster actuator test will put the

instrument cluster into its self-diagnostic mode. In

this mode the instrument cluster can perform a selfdiagnostic

test that will confirm that the instrument

cluster circuitry, the gauges, and the CCD data bus

message-controlled indicators are capable of operating

as designed. During the actuator test the instrument

cluster circuitry position each of the gauge

needles at various calibration points, illuminate each

of the segments in the Vacuum-Fluorescent Display

(VFD), and turn all of the CCD data bus messagecontrolled

indicators on and off.

Successful completion of the actuator test will confirm

that the instrument cluster is operational. However,

there may still be a problem with the CCD data

bus, the Powertrain Control Module (PCM), the

Engine Control Module (ECM), the Airbag Control

Module (ACM), the Controller Anti-lock Brake (CAB),

or the inputs to one of these electronic control modules.

Use a DRBIIIt scan tool to diagnose these components.

Refer to the appropriate diagnostic

information.

(1) Begin the test with the ignition switch in the

Off position.

(2) Depress the odometer/trip odometer switch button.

(3) While still holding the odometer/trip odometer

switch button depressed, turn the ignition switch to

the On position, but do not start the engine.

(4) Keep the odometer/trip odometer switch button

depressed for about ten seconds, until CHEC

appears in the odometer display, then release the

odometer/trip odometer switch button.

(5) A series of three-digit numeric failure messages

may appear in the odometer display, depending upon

the failure mode. If a failure message appears, refer

to the Instrument Cluster Failure Message chart for

the description and proper correction. If no failure

message appears, the actuator test will proceed as

described in Step 6.

(Sorry about the crappy formatting)

Message Description Correction

110   A failure has been identified in the cluster

  CPU, RAM, or EEPROM. 

  1. Replace the faulty cluster. 

900   The CCD data bus is not operational. 

  1. Check the CCD data bus connections at the cluster. 

  2. Check the cluster fuses. 

  3. Check the CCD data bus bias. 

  4. Check the CCD data bus voltage. 

  5. Check the CCD data bus terminations. 

920   The cluster is not receiving a vehicle speed

   message from the PCM. 

   1. Check the PCM software level and reflash if required. 

   2. Use a DRBIIIT scan tool to verify that the

   vehicle speed message is being sent by the

   PCM. 

921 The cluster is not receiving a distance pulse

   message from the PCM. 

   1. Check the PCM software level and reflash if

   required. 

   2. Use a DRBIIIT scan tool to verify that the

   distance pulse message is being sent by the

   PCM. 

940 The cluster is not receiving an airbag lamp-on

   message from the ACM. 

   1. Check the CCD data bus connections at the

   ACM. 

   2. Check the ACM fuse. 

950 The cluster is not receiving an ABS lamp-on

   message from the CAB. 

   1. Check the CCD data bus connections at the

   CAB. 

   2. Check the CAB fuse. 

999 An error has been discovered. 

   1. Record the failure message. 

   2. Depress the trip odometer reset button to

   continue the Self-Diagnostic Test.

 

[bnbrown]

I will give that a try tonight, tried it last night but then remembered the PCM wasn't plugged in, so no surprise error 920 and 921 were thrown (in addition to no bus)
of course the truck is at work not at home, an hour away.
Thanks for the info.