C1145 & C1939

[EmmaEatUraz]

Keeping this short and sweet

Currently tested
-ABS Sensor voltage unplugged: .3v to .7v when rotating wheel by hand
-ABS Sensor voltage at ABS terminal: .1v ~ .3v when rotating wheel by hand
-OHMs from ABS Terminal to Wheel Speed sensor: >.1ohms
-Voltage from ABS Terminal to Wheel Speed sensor: 2.3v~2.5v and 0 on other line.
-Fuses

Questions
What should I test next?
Why is there a voltage drop from terminal to sensor although the wiring shows no resistance?
Do you think replacing the sensor will fix the issue?

 

[Curious Hound]

The reluctant wheel (toothed wheel) on the rotating assembly does not produce a voltage in the sensor. It changes the current flowing through the magnetic coil in the sensor, by altering the magnetic field produced by the coil. So, your minute voltage readings while turning the wheel are pretty close to meaningless. Don't get worried about them.

The ABS controller sees the change in current from the sensor and turns that into pulses for the rest of the system to work with.

If your reluctant wheel and sensor are clean and free of ferromagnetic debris and you have continuity in the cable and connections back to the ABS controller, that should be fine.

I have no idea what those codes are and will have to look them up before commenting further.

 

[EmmaEatUraz]

C1939 Ford Code - Brake Pressure Switch Input Circuit Failure
C1145 Ford Code - Right Front Wheel Speed Sensor Input Circuit Failure

I am beginning to think it may be the controller its self. C1145 has been around for a while for me and ive been researching for 2 months now trying to find a solution. C1939 only appeared yesterday after I realigned my shift needle (there's no way I knocked any connections loose doing this).

 

[Curious Hound]

Is your brake reservoir full?

Here is a link to a diagnostic procedure posted in a different thread for the 1939 code.

help! 1676 and 1939 code...

changed out some dash lights and noticed the abs light bulb was burnt out, too...come to find out ive got a B1676 (batt pack volt out of range)and C1939 (brake pressure switch circuit fail) code. apparently, i bought the truck with the abs light burnt out and just caught it. ive searched here...

www.therangerstation.com

 

[EmmaEatUraz]

I also assumed it may be that. But that is full (1/8" under line).

Thx for the link to that report. Ill look at it now.

 

[sgtsandman]

As far as the speed sensor error, there could be a few different causes.

Rust and dirt build up on the reluctor ring on the rotor or the sensor.

Rust jacking causing the sensor to misalign. It doesn't take much. You would need to remove the sensor from the knuckle so you can clean up the surface that the sensor mounts to. Getting the sensor out can be easier said than done since it could be rust locked into the knuckle. You may have to destroy the sensor in order to get it out and replace it anyway but necessary in order to fix the rust jacking issue.

Wiring. The wires to the sensor have gotten damaged somewhere either on the sensor itself or the wire harnness of the truck. Don't ignore the connector itself having an issue.

From what I've seen, those are all the usual suspects. It is possible that the sensor itself is bad but verify none of the other things are the problem. Otherwise, you could be throwing a part at the problem that isn't the fix.

 

[JMDone]

1990 2.9L XLT. A different ABS sensor problem. Before changing out the sensor, as soon as the ignition was turned on, the ABS sensor error light came on and stayed on. After changing out the sensor, turning on the ignition, the error lights comes on, goes out for a second, then comes back on and stays on. Rechecked that the connector is on tight and clipped into the sensor.
Would appreciate troubleshooting advice on this and hope that on/off/on is the diagnostic clue I need.

 

[JMDone]

Finally realized the basic issue to my surprise, (as should have checked first although an unlikely one ), the master brake cylinder level sensor cable is missing! Now the trick is to find out where I can source one of those as may not be too common a replacement.

 

[JMDone]

Is the brake reservoir level sensor harness connector mounted directly below the master brake cylinder and in a group of 3 connectors? The connector towards the engine has nothing plugged into it!.

 

[JMDone]

And just to keep it interesting for me, the brake reservoir connector has three pins on it and the empty connector on the wiring harness has only two wires on a 7 pin connector. One wire is green and the other is green black. Tying now to see if there is a wiring diagram matching those two wires as the one from Ford has three wires of different colors. Local salvage yards do not have any vintage Ford rangers, broncos, aerostars, or F series, so no easy fix that route.