P2135 Code: Throttle/Pedal Position Sensor A/B Voltage Correlation (GM Guide)

P2135 is "Throttle/Pedal Position Sensor/Switch A/B Voltage Correlation." Two sensors that are supposed to agree about where the throttle is have stopped agreeing, so the module can no longer be sure what you are asking for — and it drops the vehicle into Reduced Engine Power to prevent unintended acceleration. GM issued a special coverage naming this exact code, and its repair instruction contains a distinction worth real money: on Hitachi throttle bodies, GM says the sensor kit alone corrects the fault, and the complete assembly is only fitted if that does not work.

What Does P2135 Mean?

There is no cable between your accelerator pedal and the throttle plate. The pedal is a sensor, the throttle is a motor, and a control module sits between them deciding how far to open it.

Because a fault in that chain could theoretically open the throttle when nobody asked, the system is built with redundancy. The throttle body contains two position sensors, and their voltages are expected to track each other in a predictable relationship as the plate moves.

P2135 sets when those two signals stop agreeing — typically for more than a couple of seconds. The module now has two sources telling it different stories about where the throttle actually is, and it cannot tell which one is lying.

Its response is deliberately conservative: Reduced Engine Power. Throttle authority is limited, speed is capped, and you get a warning message. That is not the fault damaging your engine — it is the safety architecture doing exactly what it was designed to do when it loses confidence in its own sensors.

Which is why the fix is almost always electronic rather than mechanical. Nothing is usually wrong with the engine at all.

The Special Coverage That Names This Code

Most codes are not named in a GM warranty programme. This one is — and it is worth understanding precisely, because the details decide whether it helps you.

Special Coverage 14582 (September 2015), titled "Special Coverage Adjustment – Throttle Body – Reduced Power Mode," describes the condition plainly: the throttle-position sensor may cause the engine to run rough, cause the malfunction-indicator lamp and/or an engine reduced power message to illuminate, and reduce the engine's power.

The entry criterion is explicit, and P2135 is first on the list:

With a scan tool, verify that DTC P2135, P0121 OR P0221 is set as Current or in History. If DTC P2135, P0121 OR P0221 is NOT set as Current or in History, no further action is required.

The coverage runs 10 years or 120,000 miles (193,000 km) from the date the vehicle was originally placed in service, whichever comes first, regardless of ownership, and the repairs are made at no charge.

Vehicles named (verified from the bulletin):

Brand	Models and years
Buick	Allure 2008–2009 · Enclave and LaCrosse 2008–2012 · Lucerne 2009–2011 · Regal 2010–2012
Cadillac	CTS and SRX 2008–2011
Chevrolet	Equinox and Uplander 2008–2009 · Impala 2008–2011 · Captiva 2008 and 2011–2012 · Colorado and Malibu 2008–2012 · Traverse 2009–2012
GMC	Canyon 2008–2012 · Acadia 2009–2012
Hummer	H3 2008–2010 · H3T 2009
Pontiac	G8, Montana SV6 and Torrent 2008–2009 · G6 2008–2010
Saturn	Outlook 2008 · VUE 2008–2009

Now the honest part, which many pages leave out. The newest vehicles in that list are 2012 models, and the coverage ran ten years from the in-service date. For practical purposes that term has now elapsed on every vehicle it covered. If a page tells you to march into a dealer and claim a free throttle body on a 2011 Silverado in 2026, it is setting you up for disappointment.

So why does it still matter? Three reasons:

• The bulletin contains GM's repair instruction, and that instruction can still save you money today whether or not anyone is paying but you. See the next section.
• It establishes the failure as a known GM defect, which is useful context if a shop is proposing something more elaborate.
• It carried a reimbursement provision for repairs already paid for within the term. If you paid for this repair years ago and never claimed, it costs nothing to ask.

Check your VIN with a dealer rather than relying on this or any other article. That is free and it is definitive.

Worth noting the contrast with a closely related code: our P1516 guide covers a throttle actuator code that is not an entry code for this coverage. P2135 is. If you have both, P2135 is the one that mattered.

Bosch or Hitachi — the Question That Sets Your Bill

This is the most useful thing in the bulletin, and it applies regardless of warranty status.

GM fitted throttle bodies from two suppliers, and the repair is different for each:

Supplier	GM's instruction	What that means for cost
Bosch	Replace the complete throttle body assembly and gasket. The sensor is not serviced separately	The whole assembly — the expensive path, but the only one available
Hitachi	Install the throttle position sensor kit. GM: the assembly "only needs to be replaced if the sensor kit does not correct the condition"	A sensor kit instead of a throttle body. Try the cheaper part first — that is GM's own sequence

GM names the parts directly: throttle body 12615516, and throttle position sensor kits 19259452 and 19300180.

The practical instruction: find out which throttle body you have before anyone orders anything. If it is a Hitachi unit and you are being quoted a complete assembly as the first move, that is not what GM told its own dealers to do.

GM also cautions that these are delicate parts — handle electronic throttle control components carefully, keep them clean, and do not drop them. And note that the gasket between the throttle body and intake manifold may need replacing; it comes with some service assemblies and not others, so check before you are stranded mid-job.

A further reported detail: bulletin 11-06-04-007C covers the same reduced-power condition with P2135 and describes replacing the throttle position sensor cover and terminals, and is reported to require an ECM reprogram on 2009–2011 models. We could not open that bulletin, so treat the reprogramming requirement as corroborated rather than verified — but it is worth asking about, because a repair that needs programming is not finished when the part is bolted on.

Reduced Power Is a Safety Feature — and a Safety Problem

Both halves of that are true and worth stating.

The feature: when the module cannot trust its throttle position sensors, limiting authority is exactly right. The alternative — acting on a signal that might be wrong — is unintended acceleration. The system is behaving correctly.

The problem: reduced power arrives without warning, and it can arrive while you are merging, overtaking or climbing. Owner complaints filed with NHTSA on the affected platforms describe sudden reduced power in traffic and stalling at highway speed. A vehicle that abruptly will not accelerate in a gap you have already committed to is a genuine hazard.

So the honest urgency answer is: this one does not wait. The vehicle is drivable in the narrow sense that it moves, but reduced power mode is intended to get you somewhere safe, not to commute in. Some owners find that cycling the ignition restores normal power temporarily — that is not a repair, and the fault will return, usually at a less convenient moment.

Several owners also report the fault appearing more readily in cold weather, which fits a marginal electrical connection contracting. If yours is intermittent and cold-biased, mention that to whoever diagnoses it.

P2135 Is the Throttle, Not the Pedal

A distinction that prevents an expensive wrong turn.

The redundancy exists in two places: two sensors in the throttle body, and two sensors in the accelerator pedal assembly. Both can disagree, and they set different codes.

• P2135 — the two throttle position sensors disagree. The part in question is at the throttle body.
• P2138 — the two accelerator pedal position sensors disagree. The part in question is the pedal assembly.

They produce the same headline symptom — reduced engine power — which is why they get confused. But replacing an accelerator pedal assembly for a P2135 is buying the wrong part. Check which code you actually have before ordering.

Symptoms of P2135

• Reduced Engine Power message and severely limited acceleration — the defining symptom
• Check engine light on
• Rough or high idle, or stalling at stops
• Hesitation, surging or unresponsive throttle
• Harsh shifting as the transmission responds to the limited throttle
• Traction control or StabiliTrak warnings alongside
• Symptoms that come and go, sometimes clearing on an ignition cycle
• A cold-weather bias in some reports

Causes and How to Confirm Each

Cause	How to confirm it	Notes
Failed throttle position sensor	Monitor TP Sensor 1 and 2 voltages on a scan tool while slowly depressing the pedal. They should track each other smoothly with no dropouts or flat spots	The dominant cause. GM's coverage exists because of it
Chafed, melted or backed-out throttle body connector	Visually inspect the connector and harness for damage, corrosion and pushed-back pins	Cheap. Check before condemning the sensor, and reroute away from heat
Poor connection worsening when cold	Note whether the fault is cold-biased — that pattern fits a marginal contact	Intermittents are easier to find with this clue
Carbon build-up affecting plate movement	Inspect the bore and plate with the duct off. See our P1516 guide for the cleaning-plus-relearn procedure	More typical of P1516, but related hardware
Accelerator pedal position sensor	Only if the code is P2138 rather than P2135	Different part — confirm the code first
Missing ECM calibration	Ask the dealer to check against your VIN	Reported as required on some 2009–2011 applications
Wiring, ground or supply fault	Circuit testing where the sensor itself checks out	Companion codes P0121, P0122, P0221, P0223 point here too
Poor-quality aftermarket throttle body	Establish what was fitted, especially if the code returned quickly	These are calibrated assemblies

How Is P2135 Diagnosed?

1. Confirm it is P2135 and not P2138. One is the throttle, the other the pedal, and they need different parts.
2. Record all codes, current and history. P0121 and P0221 alongside are the other special coverage entry codes.
3. Check your VIN against Special Coverage 14582 with a dealer. The term has likely elapsed, but this is free to ask and there was a reimbursement provision.
4. Identify whether your throttle body is Bosch or Hitachi. This decides whether a sensor kit is an option or the whole assembly is required.
5. Inspect the throttle body connector and harness for chafing, melting, corrosion and backed-out pins before touching anything else.
6. Monitor TP Sensor 1 and 2 voltages through a slow full pedal sweep. Look for dropouts, flat spots or signals that stop tracking each other.
7. On a Hitachi unit, fit the sensor kit first — GM's own sequence — and only move to the complete assembly if that does not correct it.
8. Ask about an ECM calibration where the application calls for one.
9. Perform the idle relearn after any throttle body service, and road test through the conditions that triggered the fault, including cold starts if it was cold-biased.

Parts and Cost

Repair	What it involves	Cost picture
Connector or harness repair	Where chafing, melting or backed-out pins are the fault	The cheapest outcome. Check first
Throttle position sensor kit (Hitachi)	GM parts 19259452 or 19300180. GM's instruction is to try this before the assembly	Substantially less than a throttle body. The saving this page exists to surface
Throttle body assembly (Bosch)	Complete assembly plus gasket — GM part 12615516 among others by application	The larger repair, and the only route on Bosch units
Gasket	Included with some service assemblies, not others	Check before starting
ECM reprogramming	Where the application requires it	Dealer operation; no parts
Idle relearn	Required after throttle body service	Needs a capable scan tool
Repair under special coverage	Where a VIN somehow remains in term, or a past repair qualifies for reimbursement	Potentially no charge — worth the phone call
Accelerator pedal assembly fitted in error	What happens when P2135 and P2138 get confused	Money spent with the fault still present

Order against your VIN. The Bosch and Hitachi split means part numbers are not interchangeable between otherwise identical-looking vehicles.

GM Documents That Name P2135

Document	Subject	Status
Special Coverage 14582 (Sep 2015)	"Special Coverage Adjustment – Throttle Body – Reduced Power Mode." Throttle-position sensor causing rough running, MIL, reduced power message. Entry criterion: DTC P2135, P0121 or P0221 current or in history — if none is set, no further action. 10 years / 120,000 miles from in-service date, regardless of ownership. Bosch: replace complete assembly and gasket. Hitachi: install sensor kit; replace assembly only if the kit does not correct it. Parts 12615516, 19259452, 19300180	A long list of 2008–2012 Buick, Cadillac, Chevrolet, GMC, Hummer, Pontiac and Saturn vehicles — verified. Term has now elapsed for practical purposes
11-06-04-007C	Reduced engine power with P2135. Replace the throttle position sensor cover and terminals; reported to require an ECM reprogram on 2009–2011 models	Corroborated — not opened
Special Coverage 11273 / 11273A	The earlier throttle programme this one superseded, also entered on P2135	Corroborated — superseded by 14582

Have a dealer check your VIN against current bulletins and coverages rather than relying on any article, including this one.

What Other P2135 Pages Get Wrong

• Missing the Bosch/Hitachi split. GM's own bulletin says Hitachi units need only the sensor kit, and the complete throttle body only if that fails to correct it. Quoting an assembly first on a Hitachi vehicle ignores the manufacturer's instruction and costs the customer money.
• Claiming the coverage is still active. 14582 covered 2008–2012 vehicles for 10 years from in-service date. That has run out. Telling people to demand a free repair sets them up for a bad conversation — the useful angles now are the repair instruction and the reimbursement provision.
• Or ignoring the coverage entirely. The opposite error. The bulletin names P2135 as an entry code and documents GM's own repair sequence, which is still the cheapest correct path.
• Confusing P2135 with P2138. One is the throttle body sensors, the other the accelerator pedal sensors. Same symptom, different parts.
• Treating reduced power as merely annoying. It arrives without warning and owners have reported it in traffic and at highway speed. It is a protective mode, not a mode to commute in.
• Skipping the connector inspection. Chafed, melted or backed-out pins at the throttle body produce this code with a healthy sensor, and cost a fraction of any part.
• Forgetting the relearn and the calibration. A throttle body fitted without the idle relearn, or without a required ECM update, is a repair that is not finished.

Frequently Asked Questions

Is there a warranty extension for P2135?

There was. GM Special Coverage 14582 named P2135 as an entry code and covered a long list of 2008–2012 vehicles for 10 years or 120,000 miles from the in-service date, regardless of ownership. Those terms have now elapsed. It is still worth checking your VIN with a dealer, and the bulletin carried a reimbursement provision for repairs already paid for within the term.

Do I need a whole new throttle body?

Not necessarily — it depends on the supplier. GM's instruction is that Bosch units are serviced by replacing the complete assembly, while Hitachi units only need the throttle position sensor kit, with the assembly replaced only if the kit does not correct the condition. Find out which you have before anyone orders a part.

Why did my truck go into Reduced Engine Power?

Because the two throttle position sensors stopped agreeing, so the module cannot be certain how far the throttle is open. Limiting power is the designed response to that uncertainty — the alternative would be acting on a signal that might be wrong.

Can I drive with P2135?

Only as far as you need to. Reduced power mode exists to get you somewhere safe, and it can engage without warning while you are merging or overtaking. Owners have reported it in traffic and at highway speed. Cycling the ignition sometimes restores power temporarily, but that is not a repair.

What's the difference between P2135 and P2138?

P2135 is the two sensors in the throttle body disagreeing. P2138 is the two sensors in the accelerator pedal disagreeing. They cause the same reduced power symptom but need different parts, so confirm which code is stored before ordering anything.

Could it just be wiring?

Yes, and it is worth checking first. Chafed, melted or backed-out pins at the throttle body connector produce this code with a perfectly good sensor, and repairing a connector costs a fraction of any part. Reroute the harness away from heat sources afterwards.

Why is it worse in cold weather?

Several owners report exactly that pattern. It fits a marginal electrical connection contracting as it cools and losing contact. If your fault is cold-biased, say so when the vehicle is diagnosed — it is a useful clue on an intermittent.

Do I need anything done after fitting the part?

Yes. An idle relearn is required after throttle body service, and some applications are reported to require an ECM calibration as well. A part bolted on without those steps is a repair that has not been completed.

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