OBD-II trouble code
P2158: Vehicle Speed Sensor "B"
The second speed source exists so the first one can be caught being wrong, which is why losing it usually produces no symptom the driver notices — the speedometer runs off sensor A and carries on regardless. What goes quiet instead are the functions that only run when two independent sources agree. And on plenty of vehicles there is no sensor B to replace at all: it is a value another module sends over the network.
Quick facts
- System
- Powertrain
- Category
- Transmission / Speed Sensor
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $90 – $900
- DIY difficulty
- Intermediate DIY
Browse every code in P2100–P2199, or start from the full code library.
What does P2158 mean?
P2158 is the parent code for the second vehicle speed source. It sets when the module cannot get a usable value from whatever it designates as speed sensor B — no signal, an impossible value, or a source that has stopped reporting altogether.
The question worth answering first is why a vehicle carries a second speed source at all, because the answer explains almost everything about how this code behaves. A single sensor can be confidently wrong. If the only speed input reads thirty when the car is doing fifty, nothing in the system contradicts it, and every function that depends on speed acts on a false number without hesitation. Add a second source derived from a different point in the driveline and that stops being possible: two independent measurements that disagree prove something is wrong even though neither one says which. Redundancy does not improve accuracy — it makes error detectable, and detectability is what safety-related functions are built on.
Which is why the loss of source B so often comes with no complaint from the driver. The instrument cluster is normally fed from the primary source, so the speedometer keeps working and looks entirely normal. What stops are the functions that require agreement before they will act: cruise control that refuses to engage or drops out, stability and traction arbitration that falls back to a conservative strategy, transmission shift scheduling that goes cautious, speed-dependent steering assist that stops varying, speed-sensitive door locking and wiper behaviour that quietly stop happening. Owners report a car that feels fine but has stopped doing things, and they rarely connect that to a speed sensor.
The second fact worth establishing before ordering parts is what source B physically is on this vehicle, because it varies enormously and one of the possibilities has no sensor in it. It may be a genuine second sensor on the transmission output shaft, a sensor on the transfer case or rear driveshaft on a four-wheel-drive vehicle, a speed value calculated from the ABS wheel speed sensors, or — very commonly on modern vehicles — a number that another control module measures and broadcasts on the network. In that last case there is nothing to unbolt. The fault is a communication problem, a fault in the module that sends the value, or a wheel speed sensor feeding that module, and hours can be lost hunting a sensor the vehicle does not have.
That also changes which codes should be read alongside this one. If source B is derived from wheel speed, the useful information is in the ABS module's fault memory rather than the engine module's, and a single wheel speed sensor fault will show up here as a missing second speed source. If source B arrives on the network, look for communication codes and for a module that has stopped transmitting. If it is a genuine dedicated sensor, then the ordinary chain applies — sensor, air gap, tone ring, wiring, connector.
One practical note on driveline-mounted sensors. A sensor reading a driveshaft or transfer case output lives in the dirtiest, most exposed position of any speed sensor on the vehicle, takes stone impacts and road salt directly, and is commonly disturbed by exhaust, gearbox or driveshaft work. If this code appeared shortly after anything was done underneath the car, the connector and the sensor mounting are the first things to look at and they are frequently the whole story.
Common causes
- Failed secondary vehicle speed sensor on the transmission output, transfer case or driveshaft
- Sensor connector damaged, corroded or left unplugged after underbody work
- Wiring damage from stone impact or road salt on an exposed underfloor harness
- Damaged, contaminated or loose tone ring giving no usable pattern
- Incorrect air gap after a sensor was refitted or a housing disturbed
- Wheel speed sensor fault on a vehicle where the second speed value is derived from ABS data
- Loss of the network message carrying the speed value from another module
- Failed or unpowered module that is responsible for broadcasting the second speed source
- Damaged network wiring between the sending module and the receiving module
- Metallic debris collected on the sensor tip masking the tone ring
Symptoms
- Cruise control that refuses to engage or cancels on its own
- Speedometer that continues to work normally, which is why the fault gets missed
- Transmission shifting more cautiously or holding gears longer than usual
- Stability or traction control warning light alongside the check engine light
- Speed-sensitive steering assist that stops varying with road speed
- Speed-dependent door locking, wiper or radio volume features that stop working
- ABS or wheel speed codes stored in another module at the same time
- Network or communication codes logged alongside this one
- Fault that appeared after exhaust, gearbox, driveshaft or suspension work
- No driveability complaint at all, with the code found during an unrelated scan
Diagnostic steps
- 1.Find out what source B is on this specific vehicle before ordering anything. It may be a dedicated sensor, an ABS-derived calculation, or a value another module broadcasts on the network.
- 2.If the value arrives over the network, stop looking for a sensor. Check for communication codes and confirm the sending module is powered, awake and transmitting.
- 3.Scan every module, not just the engine. A wheel speed sensor fault stored in the ABS module is a common cause of a missing second speed source.
- 4.Compare the live speed values the modules report while driving. Seeing which source is missing or frozen identifies the failed path in one road test.
- 5.If there is a dedicated sensor, inspect its connector first, especially if any underbody work has been done recently.
- 6.Check the sensor wiring along its underfloor route for stone damage, corrosion and chafe, which this position suffers more than any other speed sensor.
- 7.Remove the sensor and inspect the tip for metallic debris, damage and wear, then check the tone ring for chipped or contaminated teeth.
- 8.Confirm the air gap and mounting are correct if the sensor or its housing has been disturbed, since a sensor sitting slightly proud reads weakly or not at all.
- 9.Back-probe the sensor connector for supply, ground and signal while the wheels are turning rather than judging the circuit statically.
- 10.After repair, confirm the second source now tracks the first across the speed range, and verify the functions that went quiet — cruise control in particular — have come back.
Repair cost
$90 – $900
Diagnosis is $110 to $250 and most of that value is in establishing what source B actually is on this vehicle. A dedicated speed sensor is $60 to $200 for the part and $130 to $350 fitted, with driveline-mounted sensors at the higher end because access is awkward. A wheel speed sensor, where the second source is ABS-derived, is $150 to $400 fitted. Connector and wiring repair on an exposed underfloor harness is $120 to $400. A tone ring is cheap as a part but often requires removing a shaft or housing, which puts the job at $300 to $900. A network or module communication fault is diagnosis-heavy and part-light, and occasionally costs nothing beyond a reconnected plug.
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DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.