P0135 Code on a GMC: O2 Sensor Heater Performance, Bank 1 Sensor 1 (GMC Guide)

P0135 on a GMC is GM's "HO2S Heater Performance, Bank 1 Sensor 1" — the electric heater inside the front oxygen sensor is drawing a current the engine computer does not expect. It is a heater fault, not a sign that the sensor reads oxygen badly. On a GMC it matters because this is the sensor that runs the fuel mixture: while it is cold, the engine stays on its rich warm-up fuel table. The GMC surprise is GM's newest bulletin for it: on the 2024 Sierra 2500HD/3500HD 6.6L gas, GM found the front sensor's wiring routed against the exhaust pipe — and GM's correction is a new front sensor plus a re-route, not one or the other.

What Does P0135 Mean on a GMC?

An oxygen sensor only produces a usable signal when it is hot. Until it is, the engine control module (ECM) runs open loop on a pre-programmed fuel table that is deliberately rich. Every front sensor on a gasoline GMC therefore has an electric heater that brings it up to temperature within moments of a cold start, instead of waiting for exhaust heat.

The heater is fed ignition voltage through a fuse and the ECM switches its ground side, pulsing it to hold temperature. P0135 is GM's performance check on that heater. The circuit may be intact — no open, no short — yet the current flowing through the element is outside the window GM expects from a healthy heater. That can mean a failing element, but it can equally mean low supply voltage or a high-resistance connection starving a good heater.

Older generic code lists call P0135 "O2 Sensor Heater Circuit Malfunction." GM's current wording is "HO2S Heater Performance Bank 1 Sensor 1," and its own 2024 Sierra HD bulletin uses exactly that phrase.

How GM Tests the Heater on a GMC

GM's OBD parameter tables give the expected current window for each engine group. It is not one universal number:

The rest of the test is consistent. In the 2016 table the ECM waits for the heater warm-up delay to complete, needs system voltage above 10 V (11 V in the 2019 group 03B table), the heater duty cycle above zero and those conditions held for more than 120 seconds. It then runs one test per trip and needs 8 failures out of 10 samples. It is a Type B code, so the light normally comes on after two consecutive failing trips.

Two practical results. A heater-current figure that looks "normal" for a Terrain 1.5T can be a fault on a Sierra, so use the window for your engine. And because the test needs two minutes of steady running, a quick idle in the driveway after a repair proves nothing.

Which GMCs Set P0135

Every gasoline GMC with a heated front oxygen sensor can set it: Sierra and Sierra HD, Yukon and Yukon XL, Savana, Envoy and Envoy XL, Canyon, Terrain, Acadia, and the older Sonoma, Jimmy and Safari. On four-cylinder and turbo engines there is one bank and one front heater. On the V6 and V8 trucks and the 3.6L crossovers, P0135 is the bank 1 front heater and P0155 is the bank 2 front heater.

Duramax diesels are a separate system and are not covered here, and electric GMCs have no oxygen sensors.

The 2024 Sierra HD Routing Bulletin (24-NA-042)

GM service bulletin 24-NA-042 (revised April 2024) covers the 2024 GMC Sierra 2500HD/3500HD and Chevrolet Silverado 2500HD/3500HD with the 6.6L gas V8 (L8T). Customers may report an engine misfire or a check engine light, and technicians may find any of P0300, P0030, P0031, P0032, P0053, P0132, P0135, P0137, P0155, P0171 and P0172.

GM's cause: a mis-routed bank 1 sensor 1 oxygen sensor wiring harness that is coming into contact with the exhaust pipe. The correction is to raise the truck and inspect the wiring; if it contacts the exhaust pipe or heat shield, replace the bank 1 sensor 1 sensor (GM lists part 12679885, but says to confirm the part by VIN in the parts catalog) and route the wiring away from the exhaust. GM also notes the fuse for the circuit may be found open and need replacing.

GM does not explain each code in the list, but the pattern is what you would expect from heat-damaged wiring: heater circuit codes (P0030–P0032), heater current and resistance codes (P0135, P0053), signal codes (P0132, P0137) and, once fueling is upset, fuel trim and misfire codes. If you own a 2024 Sierra HD with the gas engine and see P0135 with any of those, ask a dealer to check the VIN for 24-NA-042 before anything else.

Older Sierra, Yukon, Envoy and Savana Bulletins

NHTSA's database lists several early-2000s GM bulletins that name P0135 on GMC trucks. We could read only NHTSA's one-line summaries, not GM's documents, so treat these as leads rather than procedures:

• Bulletin 3322 — listed for the 2004 Sierra and Yukon: "Incorrect O2 sensors and wiring harness causing HO2 sensor heater circuit codes P0135 P0141 P0155 P0161."
• Bulletin 01701 — listed for the 2004 Sierra and Yukon: 4.8L and 5.3L engines "with O2 sensor codes P0135, P0141, P0155, P0161."
• Bulletin 03-06-04-034 — listed for the 2002 Envoy and Envoy XL: service engine soon light with P0135 set.
• Bulletin 04-06-04-005 — listed for the 2001 Savana: service engine soon light with P0135 or P0155.

The common thread on the 2004 trucks is striking: all four heater codes at once, tied to incorrect sensors and harness. When every heater on a Gen III truck faults together, suspect a shared cause — wrong parts, a fuse or a supply problem — not four failed heaters. These bulletins are more than twenty years old; for practical purposes any campaign has run its course, but a dealer VIN check is free.

The Acadia Fuse Connection

GM's PIT5336 (October 2014) covers the 2013–2015 Acadia with the 3.6L LLT. It lists the front heater circuit codes P0030, P0031, P0032, P0053 and the bank 2 equivalents among about thirty oxygen sensor and purge codes, and warns the Emission 1 fuse may be found open. The cause is the bank 1 oxygen sensor harness chafing on the A/C hose coupling at the back of the engine. PIT5336 does not list P0135 itself, but because that fuse feeds the heaters, any front heater code on one of these Acadias should send you to that harness first.

For the 2016 Acadia and 2017 Acadia Limited, GM's 18-NA-009 lists P0032 (front heater control high) with front-sensor signal codes, caused by power steering fluid soaking the bank 1 O2 harness. Again, not P0135 by name — but the same sensor and wiring.

Where Bank 1 Sensor 1 Is on a GMC

• Sierra, Yukon, Savana and Envoy V8s, the 4.3L V6 and the Sierra HD 6.6L gas: bank 1 is the driver side. The sensor sits in the driver-side exhaust ahead of the converter, with its pigtail running near the pipe — the routing 24-NA-042 is about.
• Acadia 3.6L and Terrain 3.6L: bank 1 is the rear bank, toward the firewall.
• Terrain, Acadia and Canyon four-cylinders, the 2.7T and the Atlas I5/I4: one bank; the sensor sits right after the turbo or exhaust manifold.
• Envoy 4.2L inline-six: one bank and one front sensor, so P0135 is the only front heater code.

Symptoms of P0135

• Check engine light, often after a cold start and a couple of minutes of driving
• Slightly worse fuel economy, especially on short trips
• Longer than usual warm-up before the engine settles
• Misfire, rough running or fuel trim codes on a 2024 Sierra HD gas when the harness is touching the exhaust (24-NA-042)
• Several heater or O2 codes at once when a shared fuse or harness is involved
• Readiness monitors incomplete or a failed emissions inspection

Causes and How to Confirm Each

How Is P0135 Diagnosed on a GMC?

1. Record all codes. P0135 with P0155, or all four heater codes, points at a shared fuse, supply or wrong parts rather than one heater.
2. Check the VIN for bulletins — 24-NA-042 on a 2024 Sierra HD gas, PIT5336 on a 2013–2015 Acadia.
3. Check the heater fuse. If it is open, find what blew it before fitting a new one.
4. Inspect the harness from the sensor back. On trucks, look hard where the pigtail runs near the exhaust pipe and heat shield.
5. Measure supply voltage at the sensor connector with the key on and the heater commanded.
6. Check heater resistance at the sensor and compare it with the service information value for your engine.
7. Compare heater current on a scan tool against your engine's window, not a generic figure.
8. Replace the sensor only when supply, ground and wiring are good — or where a bulletin such as 24-NA-042 calls for it — using the part for your VIN.
9. Verify with real drives: GM's test needs over two minutes of qualifying conditions and runs once per trip.

Parts and Cost

GM Documents Relevant to P0135 on a GMC

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

What Other P0135 Pages Get Wrong

• "Just replace the O2 sensor." On a 2024 Sierra HD gas, GM replaces the sensor and re-routes the harness away from the exhaust — a sensor alone leaves the routing problem in place.
• Quoting one amp figure for every vehicle. GM's GMC windows range from 0.3–2.5 A (Terrain group) to 0.3–3.1 A (Sierra group).
• Ignoring the fuse and supply. A weak supply can set a performance code on a good heater.
• Treating four heater codes as four bad sensors. GM's 2004 Sierra/Yukon bulletins tie all four together to incorrect sensors and harness.
• Testing with one short restart. GM's test needs more than 120 seconds of qualifying conditions.

Frequently Asked Questions

Can I drive my GMC with P0135?

Yes in the short term. The sensor still warms from exhaust heat eventually, but the engine spends longer on its rich warm-up fuel table every cold start. On a 2024 Sierra HD gas with misfire codes alongside, get it looked at promptly — wiring touching the exhaust is not something to leave.

Is P0135 the front or rear sensor?

Front — Bank 1 Sensor 1, before the catalytic converter. The rear heater on the same bank sets P0036 or P0141.

Which side is bank 1 on my Sierra or Yukon?

The driver side. On a 3.6L Acadia it is the rear bank, toward the firewall.

Why does my 2024 Sierra HD have P0135 and a misfire?

GM's 24-NA-042 describes exactly that: the bank 1 front sensor harness routed against the exhaust pipe. The fix is a new sensor and correct routing, plus a fuse if it has blown.

Why is the light coming on a few minutes after startup?

GM's test waits for heater warm-up and over two minutes of steady conditions, then runs once per trip. As a Type B code, it usually needs two failing trips.

Should I fix P0135 before other O2 codes?

Generally yes. GM's front-sensor signal tests wait for heater warm-up, and the wide-range version of P0131 will not run while P0135 is active.

Where can I read the general version?

Our GM P0135 guide covers the code across GM brands.