|Code||Fault Location||Probable Cause|
|P050B|| Cold Start Ignition Timing Performance |
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Table of Contents
- What Does Code P050B Mean?
- Where is the P050B sensor located?
- What are the common causes of code P050B?
- How expensive is it to fix code P050B?
- What are the symptoms of code P050B?
- What are common solutions to code P050B?
- How serious is code P050B?
- How do you troubleshoot code P050B?
- Codes Related to P050B
- Get Help with P050B
What Does Code P050B Mean?
OBD II fault code P050B is a generic code that is defined as, P050B – “Cold Start Ignition Timing Performance”, and is set when the PCM (Powertrain Control Module) detects a) a failure or malfunction in the ignition timing control system, or b) an implausible or inaccurate input from one or more sensors that monitor the ignition timing when the engine coolant temperature is below a specified minimum threshold.
Note: Although trouble code P050B can afflict all OBD-II- compliant vehicles, this article will deal with code P050B as it relates to all Volvo vehicles based on the P3 chassis, and that are fitted with the 3.2L SI6 engine.
Modern Volvo engines, such as the SI6, share a common problem with all other gasoline-powered internal combustion engines, this problem being that since it is difficult to ignite a gasoline/mixture in cold cylinders, the combustion process of gasoline/air mixtures in cold engines is generally poor and incomplete, which increases harmful exhaust emissions while the engine warms up.
As a general rule, the process of combusting gasoline/air mixture becomes more efficient as the engine’s temperature rises, because the heat of the cylinder walls is partially absorbed by the air/fuel mixture during the compression stroke, which greatly assists in the smooth and orderly propagation of the combustion flame throughout the cylinder/combustion chamber.
To address the problem of poor combustion after a cold start, the engine management system compensates for low in-cylinder temperatures by advancing the ignition timing by a few degrees, relative to the engine’s base ignition timing setting. This action causes the ignition sparks on all cylinders to be delivered a few degrees of crankshaft rotation earlier than the sparks would have been delivered had the engine been hot. In addition, the fuel management system increases the fuel injectors’ pulse widths slightly to enrich the air/fuel mixture as a means to improve combustion.
Taken together, the above adaptations by the vehicle’s PCM raise the compression pressure significantly when the engine is cold, thus creating conditions in the cylinders that produce increased combustion temperatures, which in turn, greatly reduces engine warm-up times.
However, for the ignition timing control system to work as designed, the PCM uses input data from several engine sensors, including (among others), the-
- engine coolant temperature sensor (ECT)
- crankshaft position sensor (CKP)
- camshaft position sensor(CMP)
- mass airflow sensor (MAF)
- throttle pedal position sensor (TPP)
- throttle blade position sensor (TPS)
As a practical matter, the input data from the engine coolant temperature is the most critical since this sensor measures the temperature of the coolant and by extension, the engine’s temperature directly. So, assuming that all implicated sensors work as expected and that all sensor inputs fall within expected ranges, the PCM will calculate ignition timing and fuel delivery strategies to suit current environmental conditions, such as the current ambient temperature and relative humidity.
Again, assuming that the overall ignition timing control system works as expected, the calculated ignition timing and fuel delivery strategies will let the engine warm up to a point where combustion becomes stable in the shortest possible time. Put differently, the above means that once the engine coolant reaches a temperature of about 100 deg F, the PCM will begin to progressively retard the ignition timing and reduce the injectors’ pulse widths until the engine idles smoothly, even though the engine’s temperature is still well below its optimal level.
From the above, it should be clear that the engine coolant temperature sensor supplies the primary data the ignition timing control system uses to calculate cold start ignition timing and fuel delivery strategies after cold engine starts. Therefore, if the PCM receives inaccurate, implausible, or invalid input data from the engine coolant temperature sensor (which, incidentally, happens often), the PCM will recognize that it cannot manage the ignition timing control system effectively, (if at all) and it (the PCM) will set code P050B as a result.
Note: In some cases, the PCM may only illuminate a warning light if the fault persists for two or more ignition cycles.
Where is the P050B sensor located?
This image shows the location of the engine coolant temperature (ECT) sensor on a 2007 Volvo SI6 engine. In this view, the red arrow indicates the ECT sensor, while the yellow arrow indicates the thermostat housing where it attaches to the side of the engine block.
It is worth noting that this view shows the engine with the intake manifold removed to gain access to the sensor. Be aware that removing the intake manifold from an SI6 engine is a challenging procedure that requires the removal or disassembly of several major engine components. Therefore, this procedure is best left to professional and suitably qualified persons who possess the required tools, equipment, and technical knowledge to address or resolve this code.
What are the common causes of code P050B?
The most common causes of code P050B on Volvo SI6 engines could include one or more of the following-
- Defective or malfunctioning engine coolant temperature (ECT) sensor (Most common cause)
- Gross engine vacuum leaks
- Battery voltage below a specified minimum threshold
- Defective or malfunctioning thermostat
- Low engine coolant level
- Damaged, burnt, shorted, disconnected, or corroded wiring or electrical connectors in the wiring harnesses of either or both the crankshaft position (CPK) and camshaft position (CMP) sensor(s)
- Defective or malfunctioning crankshaft position (CKP) sensor
- Defective or malfunctioning camshaft position (CMP) sensor
How expensive is it to fix code P050B?
In most cases, the cost of resolving code P050B on Volvo SI6 engines at a professional workshop will run to several hundred dollars. This cost will typically consist of at least one hour’s worth of diagnostic time and up to about seven hours worth of labor, plus the costs of parts and consumables and of the charges or levies that might be payable.
Be aware though, that diagnostic time is typically charged at significantly higher hourly rates than labor charges, so be sure to obtain several price quotes/estimates that contain all relevant charges from reputable repair shops to avoid unpleasant surprises in terms of costs.
What are the symptoms of code P050B?
The most common symptoms of code P050B on Volvo SI6 engines could include one or more of the following-
- Stored trouble code and an illuminated warning light
- In some cases, multiple additional codes may be present along with P050B. Note that all additional codes relating to the crankshaft position (CKP), camshaft position (CMP) sensor, and coolant temperature sensor must be investigated and resolved before attempting to diagnose code P050B. Failure to do this will result in misdiagnoses and the unnecessary replacement of parts
- The air/fuel mixture will be excessively rich, i.e., there will be too much fuel relative to air in the mixture
- Fuel consumption will increase noticeably
- Overall engine performance will decrease noticeably
- One or more readiness monitors may not initiate or run to completion
- The idling quality may be poor until the engine warms up to its optimal temperature
- The engine may stall repeatedly after a cold start
- The engine may not run at idling speed at all in freezing ambient temperatures until the engine begins to warm up
- Depending on the nature of the problem, the engine may exhibit misfire-like symptoms upon acceleration
- The engine may or may not emit a clattering or pinging sound upon acceleration under some or all engine speeds and loads
- Fatal damage to the catalytic converter(s) could occur if code P050B is not resolved promptly
- The vehicle will not pass a mandatory emissions test
What are common solutions to code P050B?
Depending on the nature of the problem, the most common repairs for code P050B include the following-
- Replace the engine coolant temperature (ECT) sensor with an OEM or OEM equivalent part. Avoid using cheap aftermarket parts sourced online because more often than not, such parts are not calibrated for specific engines, meaning that a cheap replacement part may not work as expected
- Repair engine vacuum leaks to OEM repair standards
- Repair or replace damaged wiring to OEM standards as required
- Replace the crankshaft position (CKP) sensor with an OEM part
- Replace the camshaft position (CMP) sensor with an OEM part
Note that almost all of the above solutions require at least the partial disassembly of major engine components. Therefore, if you are not comfortable with the idea of potentially causing damage to wiring or engine components where there was none before, the wisest option would be to seek professional assistance with diagnosing and repairing code P050B.
How serious is code P050B?
Incorrect ignition timing settings caused by defects in the ignition timing control system at any engine speed and load can not only potentially cause severe to fatal damage to catalytic converters but also severe engine damage if the underlying cause(s) of the defect is allowed to persist over extended periods.
Based on the above, code P050B is considered serious, and it must therefore be resolved without undue delay.
How do you troubleshoot code P050B?
WARNING: No attempt by novice non-professional mechanics to diagnose code P050B on Volvo SI6 engines should be made without the benefit of access to-
- OEM service information, which includes relevant wiring diagrams
- OEM-specified repair procedures
- the special tools required to remove the intake manifold without damaging unrelated engine parts or components, and
- the required technical knowledge to perform relevant tests and then to interpret the test results accurately and correctly
Depending on the nature of the problem, you may need at least the following equipment to diagnose code P050B accurately on Volvo SI6 engines-
- A digital storage oscilloscope to a) test and verify the operation of the crank position (CKP) and camshaft position (CMP) sensors, and b) test and verify the operation of the ignition timing control system to confirm (or not, as the case may be), the presence of an ignition timing control fault
- A high-quality digital multimeter with at least a data-hold function to test the integrity of wiring and electrical connectors
- A Volvo-specific scan tool to scan the vehicle for Volvo-specific trouble codes that may not be accessible even to high-end generic scan tools
NOTE #1: Some of the symptoms of code P050B on Volvo SI6 engines (as listed elsewhere), can also be caused by defects that do not involve the engine coolant temperature (ECT) sensor or the crankshaft position (CPK) and/or the camshaft position (CMP) sensor(s). Therefore, we do not recommend that inexperienced non-professional mechanics attempt to diagnose code P050B if any additional codes are present on the vehicle.
Note #2: In all cases where additional or closely related codes are present along with P050B, we strongly recommend that you seek professional assistance with diagnosing and resolving all trouble codes on the vehicle to avoid even inadvertently causing potentially severe damage to the vehicle’s electrical system.
Codes Related to P050B
In many cases, one or more closely related fault codes may be present along with P050B on Volvo SI6 engines, with the codes listed below being the most common-
- P050A – “Cold Start Idle Air Control System Performance”
- P050C – “Cold Start Engine Coolant Temperature Performance”
- P050D – “Cold Start Rough Idle”
- P050E –“ Cold Start Engine Exhaust Temperature Too Low”
Note that when the above codes are present along with P050B, they will likely have set in response to trouble code P050B setting, although the setting of one or more of the above codes can also cause P050B to set.
Thus, the best way to determine whether P050B caused the other codes to set (or the other way around) is to see which code set first. For example, if code P050B is listed first on a scan tool, the other codes listed here will be set in response to P050B setting. Therefore, resolving code P050B first will usually, but not always, resolve the other codes as well.
Nonetheless, there are some exceptions to this rule: in the case of P050B, all other codes must be cleared before an attempt is made to diagnose P050B. As stated elsewhere, failing to do this will result in a misdiagnosis.
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