OBD-II trouble code
P2629: O2 Sensor Pumping Current Trim Circuit/Open (Bank 2 Sensor 1)
More money is wasted on this code before anyone picks up a tool than after. Bank 2 is defined by cylinder numbering, not by which side of the engine you can reach — and on a transverse V the two answers are frequently opposite.
Quick facts
- System
- Powertrain
- Category
- Oxygen Sensor
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $150 – $1,000
- DIY difficulty
- Advanced DIY
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What does P2629 mean?
A wideband oxygen sensor leaves the factory with a small calibration resistor built into its connector, because pump current characteristics vary from one sensor to the next and the module needs a per-sensor correction to turn raw current into a real oxygen measurement. This code says that correction is not reaching the module on the upstream sensor of bank 2 — the circuit is open.
Before any of the electrical detail matters, there is a question that decides whether the repair succeeds at all: which side of this engine is bank 2? The answer is fixed by the manufacturer's cylinder numbering. Bank 2 is the bank that does not contain cylinder number one. It is not the passenger side, it is not the far side, and it is emphatically not whichever side is easier to get a socket onto. On a longitudinal V-engine the two banks sit left and right. On a transverse V6 or V8 the banks sit front and rear, one against the radiator and one against the bulkhead, and which of those two carries cylinder one varies by engine family. Look it up for the specific engine, in writing, before ordering a part. A sensor replaced on the wrong bank leaves the fault exactly where it was and adds a healthy sensor's cost to the bill.
What the open circuit actually does depends on the fact that this is a V-engine with two of everything. The module still has a valid calibration for bank 1. It has none for bank 2. Whatever it substitutes for the missing value applies to one side of the engine only, so the two banks end up fuelled against two different standards of measurement — one real, one assumed. The engine as a whole may still idle and drive acceptably, because each bank has its own fuel control and each is doing the best it can with what it has been given. The asymmetry is the signature: a fuelling complaint that belongs to one bank and not the other, with no mechanical explanation on that bank.
The wiring itself is worth understanding because a bank 2 upstream sensor lead is not the same animal as its bank 1 twin. It is longer. On a transverse engine it either crosses the top of the engine or runs behind it, out of sight, to reach a connector the harness designer put where there was room rather than where a technician would like it. And because the sensor is bolted to an exhaust manifold that moves with the engine while the harness connector is often fixed to the body, the lead has to absorb engine rock every time the throttle is opened and closed. Service loops are designed for that, but they fatigue, and the fatigue concentrates where the loop is shortest or where a clip has fallen off and let the lead pull tight.
The rest of the cause list is ordinary connector work, with one human factor that is specific to this position. A connector reached blind, over the back of an engine, by feel, is a connector that gets pushed until it feels right rather than until it latches. Anything that has been off in the last few months — an intake manifold, a coil pack, a mount, a downpipe — puts this connector on the suspect list.
Common causes
- Connector left partially latched after work over the back of the engine, where it is reached by feel
- Fatigued conductor in the bank 2 service loop, where the lead has to absorb engine rock on its mounts
- Lead pulled tight and broken after a retaining clip was lost or not refitted
- Corroded or backed-out terminal on the trim pin in the bank 2 upstream connector
- Universal or non-specification sensor fitted, which has no individually trimmed resistor to present
- Original pigtail cut and spliced, leaving the calibration resistor on the discarded sensor
- Open trim conductor in the section of harness that crosses or passes behind the engine
- Failed calibration resistor in the connector body, or a module trim input failure, which is the least likely of these
Symptoms
- Check engine light with the car otherwise driving acceptably
- A fuelling complaint that belongs to one bank only, with no mechanical fault on that bank
- Bank 2 fuel trim codes stored alongside this one that resist a mechanical diagnosis
- Worse fuel consumption without a change in driving
- Emissions readiness monitors not completing
- Code appearing shortly after intake, manifold, mount or exhaust work
- Code returning immediately after an upstream sensor was replaced with a universal part
- Mild roughness at idle on some vehicles, and nothing perceptible at all on others
Diagnostic steps
- 1.Establish which physical bank is bank 2 on this specific engine, from the manufacturer's cylinder numbering, and write it down before touching anything. This is the step that most often decides whether the repair works.
- 2.Let the engine cool. The upstream sensor sits on the exhaust manifold and both the manifold and the sensor body stay hot enough to cause serious burns long after the engine is switched off.
- 3.Ask what has been apart recently. An intake manifold, a mount, a coil or a downpipe on that bank puts a disturbed connector at the top of the list and can end the diagnosis in two minutes.
- 4.Find and unlatch the bank 2 upstream connector properly, then look at it in good light rather than by feel: terminals seated and gripping, seal present, no green on the pins, body not cracked.
- 5.Establish what sensor is actually fitted. An original moulded connector is one thing; a generic plug, a crimped adapter or a spliced pigtail is another, and a universal part leaves this circuit open by design.
- 6.Measure resistance across the trim pins on the sensor side of the connector and compare with the manufacturer's figure. Open at the sensor condemns the sensor or its connector body; in specification moves the search into the harness.
- 7.Trace the lead along its full route, including the part that crosses or passes behind the engine. Look for a short or missing service loop, a lost clip, and insulation that has been rubbed or pulled. Flex it gently along its length while watching for a reading that changes.
- 8.With the ignition off and both ends disconnected, check continuity on the trim conductor from the sensor connector through to the module pin.
- 9.After repair, clear the codes and drive until the oxygen sensor monitors complete, then confirm that bank 2's fuel trims have settled in the same region as bank 1's.
Repair cost
$150 – $1,000
The cheap outcomes are a reseated connector at nothing more than diagnostic time, or a terminal and pigtail repair at $160 to $500. Harness repair on the trim conductor is $200 to $560, and it runs higher than the bank 1 equivalent because the damaged section is often the part that crosses or sits behind the engine. A correct original-specification upstream wideband sensor is $340 to $900 installed; the parts price matches bank 1 but the labour does not, because a rear-bank sensor on a transverse engine can need the intake or a heat shield out of the way first. Diagnostic time is $120 to $260. The expensive mistake is not any of these — it is buying and fitting a sensor for the wrong bank, which adds a full part and a full labour charge and leaves the code exactly where it was.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with oxygen sensor replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an advanced DIY job. It typically requires specialty tools, scan-tool access, lifting equipment, or careful sequencing to avoid causing new failures. Plan for extended downtime and have a backup vehicle. Most owners are better served by a shop that has done this repair before.