Hi. Since I've replaced my brake lines, I'm getting ABS and traction control lights on with DTC C0045, Left Rear Wheel Speed Sensor Circuit Malfunction.

What I've tried:
- Cleaning the ECM plug into the ABS module. It was already clean and the pins look perfect. No corrosion on them. ABS module was out for the brake line repair and was handled with care.
- Replaced left rear wheel sensor with a new one (OEM ACDelco). Tested ohms on new sensor prior to installing and it came back at 5100, about what the (working) rear right sensor outputs. Old sensor was massively rusted and gunked up. The tone ring/reluctor looks visually fine and I've verified there is no debris on it.
- If I connect a wire to the sensor wire harness and probe that wire along with the coordinating pin(s) (#22 Black and #23 Red) at the ECM plug, I get the continuity beep.
- I have examined the wire conduit (visually) and do not see any breaks.

My question:
- Is continuity the end all? I do get the continuity beep. Does this alone mean there cannot be a break in the wire running to the ECM? If not, is there a better test that can determine a wire break issue between the ECM and sensor wire harness?
- I haven't taken a AC/V reading of spinning the wheel yet. Is this only to determine if sensor is good? How do I test the tone ring/reluctor to verify that isn't the problem?

Since the sensor has been replaced, I'm at the point where it has to be either a break in the wire I'm missing , the ECM itself, or the reluctor. I'm a noob with multimeters so is there a better test than what I'm doing with continuity to test a wire issue? I don't want to have to send the ECM for repair if that is not my issue.

I have a Tech 2. C0045 is both history and current. Whatever the issue is, it will not clear out the DTC at all, even for a second. Since the new brake lines, I haven't had it in motion....all of this occurs while in park.

 

Strange things happen when you start working with the brake lines on a H2 and I have seen the system set codes that makes no sense, it sounds like you may need to perform ABS Brake Automated Bleed and Pressure Bleed using a Tech 2.

Check out this youtube:

 

I wish I could! After manually bleeding the brakes, I went to do the ABS bleed on the tech 2. But since the code was triggered, and it won't let me clear it even temporarily, it won't do the ABS bleed until the code is resolved.

 

Try removing the battery cable for 30 minutes, if this fails try the GM emergency ABS reset:
Turn you key on (but do not start). Perform 3 quick presses of your gas pedal, now start your engine, the ABS system will dump all codes and re-initialize.
At that point you should be able to attach your Tech 2 and perform the ABS Brake Automated Bleed and Pressure Bleed

 

No luck with battery disconnect or the emergency ABS reset. Neither would reset the light nor let the Tech 2 delete the code, so I still haven't been able to run the automated bleed in Tech2.

I disconnected the right rear sensor wire and plugged it into the rear left. Code for left still exists. I assume since I didn't get any codes for a right rear issue that both the new sensor that was installed and the lefts reluctor/tone ring is operating correctly and not the problem.

I checked for continuity again and have it on both wires from the ebcm connector to the left wheel speed harness connector.

I did notice that my On Star microphone is now humming/buzzing. I don't remember the specifics, but years ago I installed an aftermarket head unit and ran the on star microphone to the new headunit to use for bluetooth calling. But, I've never had it ever hum/buzz in the past. It kind of makes me think that maybe it could be a grounding issue, but I'm really not knowledgeable of electrical so I don't know. It's just something that has appeared during all of this.

I wouldn't think it would be a bad ground....the other 3 are working as they should.

 

I guess I'm getting confused....what I called the microphone is I guess the auto hvac sensor? In either case, this is what is now buzzing. Don't know if it's all related. Electrical issues are so aggravating.

 

C0045 is quite specific, this info is straight from the GM Service manual for 05 (sorry don't know your MY)

Something is forcing the EBCM into a DTC, I'd tend to believe the message is accurate. Maybe the wiring got damaged when the brake lines were replaced, as I recall there's a lot of work need around the left rear wheel and ABS module. BTW brake fluid conducts, hopefully none made it into the EBCM's internal circuitry. It's very hard to prevent brake fluid getting everywhere, especially if the lines had to be cut.. There are 3 fuses associated with the EBCM, all under the hood, but I'm sure you've checked those, anyway there would probably be other DTC's set.

Continuity is paramount as the vehicle moves, vibrates etc, cables can flex and any breaks or shorts can come and go, it only takes a fraction of a second to be detected. There are seen some good YT videos on brake sensors, might be worth some research there. However it sounds like your fault is hard (catastrophic) suggesting it's either a short or EBCM fault.

Measure the stationary voltage on the right rear sensor and compare with the left, they should be pretty much be the same. Also also with the battery disconnected, measure the sensor wires for shorts to chassis, to each other or elsewhere. If you kept your old sensor plug that back in and measure the voltage on that too. Its odd a sensor would it suddenly fail at the same time the work was done.

The SM description suggests an open circuit may not be reported immediately, whereas a short would. e.g. "A short to ground the wheel speed sensor signal circuit is shorted to ground"

Check for any crushed, pinched or cuts in the wires/harness, unplug some other wheel sensors and check the DTCs. Retrace along the areas you worked on (difficult I know) it like there's a connection between the work done and the fault.

Most of the DTC conditions apply at speed, so something it grabbing the attention of the EBCM right from the start, C0045 is summarized as "Left Rear Wheel Speed Sensor Circuit" which is the clue.

Try unplugging the wheel sensor and see if the code changes or can be cleared, if it does change, plug in the old sensor and see what happens If nothing makes any difference it does suggest either a short, something linked with the EBCM the module itself, hopefully the brake lines are all in the right places.

It's remotely possible the DTC is being reported for something else, but not likely given the EBCM has at least 15 codes from C0035 to C0267 + the generic C0550 ECU malfunction.

Suggest:-

• Set the multimeter to low ohms (typically 0-200 ohms) check by shorting the probes together it reads less than 1 ohm (basic meter check)
• Short out the sensor connector, unplug the EBCM and measure across 22 + 23, they should reading no more than a few ohms.
• Keep measuring and get someone to flex/move the harness along the route, the reading across 22 + 23 should barely change.
• Again with the connector still shorted, switch the multimeter to high ohms and check neither 22 or 23 have no reading to chassis or any other pin in the EBCM connector or elsewhere.

If everything is OK it's probably not a wiring issue.


If you do find it please let us know ✔️

FYI

Circuit DescriptionAs the wheel spins, the wheel speed sensor produces an AC signal. The electronic brake control module (EBCM) uses the frequency of the AC signal to calculate the wheel speed.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
• DTC C0045 Left Rear Wheel Speed Sensor Circuit

Conditions for Running the DTC
C0035 C0040 C0045 C0050
The ignition is ON.
C0036 C0041 C0046 C0051
• Vehicle speed is over 40 km/h (25 mph).
• The brake pedal is not pressed.
• The ABS is not active.
Conditions for Setting the DTC
C0035 C0040 C0045 C0050
One of the following conditions exists for 0.02 second:
• A short to voltage in the wheel speed sensor signal circuit.
• An open in the wheel speed sensor signal circuit.
C0036 C0041 C0046 C0051
All of the following conditions exists for 0.01 second:
• The suspect wheel speed equals zero.
• The other wheel speeds are greater than 40 km/h (25 mph) for 0.01 second.
• The suspect wheel equals zero during drive off, and the other wheels are greater than 18 km/h (11 mph).
• A short to ground the wheel speed sensor signal circuit is shorted to ground.
• A deviation of 2 wheel speeds at either side of the vehicle greater than 6 km/h (4 mph), or at the front axle greater than 10 km/h (6 mph) for a time period of 10-20 seconds.

 

So I haven't came up with anything yet.

- I get .2/.3 ohms while measuring across 22+23. No change as someone moves and wiggles the harness around.
- 22+23 have no ohm/continuity to any other pin nor chasis.

The weirdest thing is unplugging and switching sensors around.

With all plugged up to their correct position, I get C0045.
With the rear left unplugged only, I get C0045
With the rear right and rear left BOTH unplugged, I get ONLY C0050 (Rear Right). I am able to then clear out the C0045 History, and it does not show C0045 as current....only the right C0050 is current.
With the rear right harness plugged into the left rear sensor and the right sensor unplugged (left doesnt reach to plug it in there), I once again get a current C0045.

The old sensor is no longer useable. It was replaced with a new GM/ACdelco sensor after initially getting the C0045. Along with the brake line project, I also did the fuel pump at the same time, so I had the gas tank down as well. The parking brake shoes were highly rusted out, so I ended up replacing those along with new rear calipers and rotors. Due to the excess rust, getting the old sensor removed took a lot of force. Old sensor was all gunked up on the end and got destroyed in removal.

I'm still hoping it's a wire issue. The LR sensor harness was unplugged to do the brake lines. The line was unclipped over the axle for the brake line project. The ABS module was treated with care....I removed it for the brake line project. Battery was disconnected. Pin terminals were clean. It wasn't dropped...it was babied. If there is a problem in the module/EBCM I don't understand at all. My error is with the wiring mess and sensor I had to mess with to do the brake lines. It's now the problem area. But I can't detect any fault while testing this wiring.

 

ThePtero great work, very good diagnostics.

Also sounds like you did a really good job on the brake system and fuel pump (was this also worth doing?)

From your analysis, it seems DTC's C0045-left or C0050-right are generated for "open circuit" as well as "short-circuit" conditions, which is logical but sadly we can't tell which.

Shame the old sensor can't be plugged-in (not mounted) just needed an "impedance" for testing. Not sure, but you could try poking in a 5100 ohm resistor (i.e. what you measured previously) where the sensor should be, it might fool the ECU into thinking there's a sensor in circuit.

Compare the left & right sensors:-

• Measure the resistance of the sensor pins and compare, they should both be similar.
• Measure the resistance of each pin to the sensor-body and compare, again they should both be similar.
• Inspect the sensor plug, maybe the pins are not making contact when mated, confirm by measuring the circuit resistance at the ECBM (5100 ohms)

The priority and order of the ECBM's reporting is unknown to me i.e. which come 1st "open" or "short", and which wheel, however "shorts" may take priority over "opens" followed by wheel order.

Auto-bleed runs clockwise i.e. FL,FR,RR,RL so this may be wheel order too and "shorts" may take priority, all this suggests the rear-left wiring is the problem.

Check also the new sensors p/no against model year.

Also remembered a previous thread here.

Hope you find it 🤞

 

Man… idk but I’m literally doing brake lines right now. I hope I don’t run into this. It wouldn’t be out of character for my h2.