2nd Gen Non-Engine/Transmission No Speedometer

[n7gxz]

My speedometer died the other day. It went to zero and then every now and then it would pop to life for a moment or two and then die again and then final nothing at all. I have a special rally computer that is tied in to the data link between the CAB (Controller Anti-lock Brake, 4-wheel ABS) and the PCM and it is not seeing any signal. I’ve replaced the read axle sensor and the CAB but still no speedometer and now the ABS light is flashing once a second.



Anyone have any ideas? Replace the front wheel sensors? Truck has 167K on it.



Kevin

 

[JLandry]

Kevin,



AFAIK, the front axle sensors have nothing to do with the speedometer.



Troubleshooting ideas:



Make sure there's no problem with the connector at the rear wheel speed sensor. I vaguely recall reading of others having problems there.



Also, if you haven't already done so, try temporarily disconnecting the rally computer just to rule out it as the cause... you wouldn't think it could be, but you can't know for sure unless you try it.



Next, I think I'd test the continuity of the wiring between the rear wheel speed sensor and the CAB. To do this, disconnect CAB connector C1 (the larger of the two connectors) and connect a jumper wire between pins 1 and 8... maybe a paper clip would work. Then back at the rear wheel speed sensor, disconnect the plug and use an Ohmmeter to verify there's a complete low-resistance circuit between the two connector pins.



If that doesn't turn anything up, the next test will verify if the new rear speed sensor you installed is actually working properly. Be sure you've reconnected the plug at the rear wheel speed sensor, then disconnect CAB connector C1 again. Jack up the rear axle of the truck so both wheels are off the ground. Have a helper spin the rear wheels at approximately 1 revolution per second (or start the truck and let it idle in drive after taking all the necessary safety precautions to make sure it can't move forward). Using an AC voltmeter, measure across pins 1 and 8 of CAB connector C1. You should see an AC voltage reading above 365 mV while the wheels are rotating.



If you're getting the correct reading from the rear wheel speed sensor, then presumably the CAB is bad. If you didn't see the correct reading, then presumably the rear wheel speed sensor (or the wiring harness) is faulty.



Once you've found and fixed the problem, you'll need to clear all the DTC's (Diagnostic Trouble Codes) that have undoubtedly been set in the PCM to get the ABS light to quit flashing.



Good luck,



John L.

 

[n7gxz]

Thanks John I'll give things a try when I get home.



Kevin

 

[JLandry]

Kevin,



I said: "If you didn't see the correct reading, then presumably the rear wheel speed sensor (or the wiring harness) is faulty. "



After I saved my post earlier, I realized the above statement is only partially correct. You could also have a problem with the tone wheel inside the rear differential (loose or missing teeth), and/or it's also possible the speed sensor tip doesn't have the correct air gap from the tone wheel. Obviously those would be the last things you'd want to check.



Best regards,



John L.

 

[Missouri Mule]

Your speedometer could be at fault also. My Freightliner speedometer was acting up and as I recall finally quit. My mechanic checked the speedometer and replaced it (My tach still acts up but hasn't quit).

 

[JLandry]

Your speedometer could be at fault also.

That possibility can quickly be eliminated by conducting an "actuator test" on the instrument cluster:

ACTUATOR TEST



The instrument cluster actuator test will put the

instrument cluster into its self-diagnostic mode. In

this mode the instrument cluster can perform a self diagnostic

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 message controlled

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 DRBIII 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.



(6) The instrument cluster will begin the Vacuum

Fluorescent Display (VFD) walking segment test.

This test will require the operator to visually inspect

each VFD segment as it is displayed to determine a

pass or fail condition. First, all of the segments will

be illuminated at once; then, each individual segment

of the VFD will be illuminated in sequence. If any

segment in the display fails to illuminate, repeat the

test to confirm the failure. If the failure is confirmed,

replace the faulty instrument cluster. Following completion

of the VFD walking segment test, the actuator

test will proceed as described in Step 7.



(7) The instrument cluster will perform a bulb

check of each indicator that the instrument cluster

circuitry controls. If the wait-to-start indicator does

not illuminate during this test, the instrument cluster

should be removed. However, check that the

incandescent bulb is not faulty and that the bulb

holder is properly installed on the instrument cluster

electronic circuit board before considering instrument

cluster replacement. If the bulb and bulb holder

check OK, replace the faulty instrument cluster.

Each of the remaining instrument cluster circuitry

controlled indicators except the cruise indicator are

illuminated by a Light Emitting Diode (LED). If an

LED or the cruise indicator in the VFD, fails to illuminate

during this test, the instrument cluster must

be replaced. Following the bulb check test, the actuator

test will proceed as described in Step 8.



(8) The instrument cluster will perform a gauge

actuator test. In this test the instrument cluster circuitry

positions each of the gauge needles at three

different calibration points, then returns the gauge

needles to their relaxed positions. If an individual

gauge does not respond properly, or does not respond

at all during the gauge actuator test, the instrument

cluster should be removed. However, check that the

gauge terminal pins are properly inserted through

the spring-clip terminal pin receptacles on the instrument

cluster electronic circuit board before considering

instrument cluster replacement. If the gauge

terminal connections are OK, replace the faulty

instrument cluster.



(9) The actuator test is now completed. The instrument

cluster will automatically exit the self-diagnostic

mode and return to normal operation at the

completion of the test, if the ignition switch is turned

to the Off position during the test, or if a vehicle

speed message indicating that the vehicle is moving

is received from the PCM on the CCD data bus during

the test.



(10) Go back to Step 1 to repeat the test, if

required. ​

 

[WStephens]

When I still had the 99 the speedo quit and the dealer did not know what the cause was but they reprogramed the tire size to what I was running and it took care of the problem.

 

[p-Bar]

When I had my 99 it was the speedo sensor in the rear end . I also assume your ABS light is on that will go away since it needs the speedo to function properly. Good luck

 

[ToolManTimTaylor]

Also a P0500 code will also give a hint to a VSS issue (Vehicle speed sensor)

 

[n7gxz]

I got the problem figured out. It turned out to be the rally computer input data cable which taped into the speedometer data line between the ABS and the PCM. A loose/short in the RJ-45 connector.



There where no DTC's posted because of this which made things a little harder to figure out.



Thanks for everyones help and suggestions.



Kevin

 

[Udaloy]

I am now having this issue myself. Three days ago I changed the clock forward one hour. Two days ago, I noticed that the clock was off by 2. 5 hours when I went to lunch. Last night I installed a set of KC lights, and on my first trip out I had no speedometer, parking brake light and ABS light's are on.



I went out this morning and noticed one of the nuts on the positive battery post wasn't tight, so fixed that. No difference. I ran the actuator test, but didn't receive any numbers like are listed above. I received the following:



C-CODE

21 18

A4 38

A7 67

AA 67

AC 00

00 00



The lights are on a simple rocker switch setup with a relay, not run with the head lights in any way (the KC's are located in my rear bumper). We're grounded to the negative post of the battery and we're drawing power straight from the battery as well. I don't see how adding the lights would make this happen, but I don't believe in coincidences. I'll go see if I'm getting any error codes and post what I find.

 

[Udaloy]

Sorry all, I didn't realize I was in the 2nd gen forum. I'll go post in the 3rd gen.