Speedometer not working

[75motorhd]

2024 CX-5, non-turbo.
It appears that my speedometer does not respond do the summer heat. It works fine in the morning, but in the afternoon it stops responding.
Battery has been load test and works normally. No codes are found when I read the ODB port. Cruise control still works fine so I have reason to think the speed sensor is the cause.
Does anyone know of what connectors I need to check before tearing apart my dash?

 

[cz5gt]

2024 - Your car is under full 3/36 warranty. Would recommend to go to a Mazda dealer to sort this out.

 

[75motorhd]

2024 - Your car is under full 3/36 warranty. Would recommend to go to a Mazda dealer to sort this out.

Dealer is a last resort.

 

[stickerbush]

Dealer is a last resort.

Wow. You would "tear apart your dash" before going to a dealer for a warranty repair? Wow.

What makes you believe that there is such a part as a "speed sensor" in the CX5? I suggest you get a copy of the shop manual and wiring diagrams and spend some time studying before trying to fix this.

 

[ADS-B]

Wow. You would "tear apart your dash" before going to a dealer for a warranty repair? Wow.

What makes you believe that there is such a part as a "speed sensor" in the CX5? I suggest you get a copy of the shop manual and wiring diagrams and spend some time studying before trying to fix this.

“Tearing” apart the dashboard it’s relatively easy. Start from the right hand side/ passenger side.

 

[Mazdiod2]

I would guess some kind of bad connection that opens because of heat but I have no idea where to look. If you don't want to take it to a dealer I wonder if it would be a good idea to call one and ask about it.

 

[stickerbush]

Here's what Chat GPT has to say about this issue.

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If your Mazda CX-5 speedometer stops working in hot weather but shows no check engine light or error codes, you're likely dealing with a temperature-sensitive electrical or sensor issue. Here are the most probable causes and how to investigate them:

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Likely Causes of a Speedometer Failing in Heat​

1.​

• Function: Sends speed data to the instrument cluster and ECU.
• Heat Sensitivity: A failing sensor or its wiring may only misbehave when it gets hot.
• Why No CEL?: Some VSS failures don't trigger a code unless they're completely non-functional or affecting shift points.

Test:

• Mechanic can check VSS signal with a scan tool during a hot road test.
• Look for intermittent dropouts in the vehicle speed signal.

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2.​

• Function: The cluster receives speed data and displays it.
• Symptoms: If only the speedometer is affected (not the odometer or other gauges), it may be a stepper motor issueor heat-sensitive solder joint.

Signs:

• Tap or press near the gauge to see if it temporarily "wakes up."
• Monitor whether other gauges flicker, dim, or misbehave in heat.

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3.​

• Heat expands metal and plastic, possibly breaking connection in a frayed or loose wire.
• Particularly vulnerable points: VSS wiring, ECU connectors, or behind the dashboard.

Inspect:

• Look for cracked insulation, greenish corrosion, or melted-looking plugs.
• Shake-test the harness near the VSS while monitoring speed data with a scan tool.

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4.​

• Weak or corroded ground near the sensor, cluster, or PCM can cut off or scramble the signal.
• Hot weather increases resistance in corroded connections, which may cause intermittent failure.

Tip:

• Check battery terminals, ground straps, and the main chassis grounds.
• Especially check the G101 or G201 ground (depending on model year) tied to the instrument cluster.

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Less Likely But Worth Mentioning​

• Software glitch: Uncommon, but a firmware update (especially on 2017–2019 models) might fix bugs in gauge logic.
• Brake light switch issue: Occasionally causes erratic VSS input, but typically triggers transmission or cruise issues too.

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What to Do Next​

1. Scan with live data (not just codes) to check for missing or erratic speed readings when hot.
2. Check continuity and voltage on the VSS circuit when the car is warm.
3. Test cluster functionality — some shops can bench test clusters for heat sensitivity.
4. Inspect grounds and wiring harnesses, especially around the transmission and fuse box.

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Professional Tip:​

Ask your mechanic for a scan tool that can display live MPH from the ECU. If the ECU sees speed but the cluster doesn’t, it’s a cluster issue. If no speed shows at all, it’s VSS or wiring.

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Would you like help finding a service bulletin for your CX-5 model year or wiring diagrams for the VSS circuit?

You said:​

where is vss located

ChatGPT said:​

The Vehicle Speed Sensor (VSS) on a Mazda CX-5 is typically located on the transmission housing, near the axle shaft or output shaft. The exact position depends slightly on the model year and engine/transmission configuration, but here’s a general guide:

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​

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• Mounted on the top or side of the transmission, close to where the drive shafts exit.
• Usually held in by a 10mm bolt and has a 2- or 3-wire electrical connector.
• May be near or under air intake ducting or battery tray, depending on layout.

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VSS vs. Wheel Speed Sensors​

Note: On newer Mazdas (especially 2017+), some speed data may come from ABS wheel speed sensors, not a dedicated VSS.

• These are located at each wheel hub.
• The ECM can calculate vehicle speed by averaging wheel sensor data.
• If you're not seeing codes, and the speedometer is the only issue, it’s more likely a problem with:
  
  • Instrument cluster
  • Wiring
  • Central control module

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How to Locate It (If You Have a Traditional VSS)​

1. Look down behind the engine toward the transmission bell housing.
2. Find the output shaft area (where the drive axles go into the transmission).
3. Look for a small, usually black plastic sensor with a wiring plug attached.

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Tools You May Need​

• Flashlight or inspection mirror
• 10mm socket and ratchet
• Multimeter (to test voltage/signal)
• OBD2 scanner with live data capability

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[Odrapnew]

Since the cruise control still works, I would say it's LESS LIKELY to be a speed sensor.
CC needs to know vehicle speed to control it, so the ECU is still able to see the vehicle speed.
If it were me, Issue + warranty = dealer

 

[Mazdiod2]

Since the cruise control still works, I would say it's LESS LIKELY to be a speed sensor.
CC needs to know vehicle speed to control it, so the ECU is still able to see the vehicle speed.
If it were me, Issue + warranty = dealer

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Ask your mechanic for a scan tool that can display live MPH from the ECU. If the ECU sees speed but the cluster doesn’t, it’s a cluster issue. If no speed shows at all, it’s VSS or wiring.

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The Chat GPT is impressive. I know I would check while driving with a OBCII "Scangauge' or "Ultragauge' to see what the ECU is reporting.