P133E – Cylinder 7 Glow Plug Offset Exceeded (Chevrolet)

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By Reinier (Contact Me)
Last Updated 2023-10-02
Automobile Repair Shop Owner
CodeFault LocationProbable Cause
P133E P133E – Cylinder 7 Glow Plug Offset Exceeded (Chevrolet)
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Manufacturer Specific Definitions for P133E

MakeFault Location
ChevroletCylinder 7 Glow Plug Offset Exceeded

Table of Contents

  1. What Does Code P133E Mean?
  2. Where is the P133E sensor located?
  3. What are the common causes of code P133E?
  4. What are the symptoms of code P133E?
  5. Get Help with P133E

What Does Code P133E Mean?

OBD II fault code P133E is a manufacturer-specific trouble code that is defined by carmaker Chevrolet as P133E – “Cylinder 7 Glow Plug Offset Exceeded” and is set when the PCM (Powertrain Control Module) detects an abnormal or unexpected high electrical resistance in the glow plug of cylinder #7 when the glow plug is hot. Note that this code only affects Chevrolet vehicles with diesel engines.

The only function that glow plugs on diesel engines have is to provide a source of intense heat to assist in igniting the diesel/air mixture when the engine is cold because diesel combustion is extremely inefficient at low engine temperatures.

Unlike earlier iterations of glow plug control systems that supplied all the glow plugs with equal amounts of power at the same time regardless of the condition of the glow plugs, modern glow plug control systems supply individual glow plugs with different amounts of power based on the electrical resistance of each glow plug.

This arrangement has several practical advantages, including that all the glow plugs reach the same temperature in approximately the same amount of time and that all the glow plugs reach their optimal temperature in less than about three seconds. By way of contrast, consider that the glow plugs on older glow plug systems could take up to ten seconds or more to reach their optimal temperature.

In terms of operating principles, modern computer-controlled glow plug control systems use dedicated leads, much like spark plug leads on gasoline engines, to connect each glow plug to the overall control system. In practice, when the glow plug control system is activated when the vehicle is switched “ON”, the glow plug control module measures the electrical resistance of each glow plug. If all the glow plugs are fully functional, they will (theoretically) all have approximately the same electrical resistance but in practice, small manufacturing differences and some in-cylinder operating conditions mean that it rarely happens that all the glow plugs have the same electrical resistance.

Nonetheless, based on the electrical resistance of each glow plug, the glow plug control module will apply a pulse-width modulated electrical signal to each glow plug that is calculated to heat each glow plug to the same temperature in the same amount of time as all the other glow plugs. Put differently, this means that the voltage the glow plug control module supplies to some glow plugs may be several percentage points higher or lower than the voltage it supplies to other glow plugs, but the net effect of the different voltages is that all the glow plugs are heated to the same temperature in the same amount of time- give or take a few hundredths of a second each way.

As a practical matter, the above means that a) engine cranking and starting times are reduced significantly, and b) harmful diesel exhaust emissions are also reduced measurably.

However, the proverbial devil lives in the detail and in this case, the detail involves the fact that the electrical resistance of each glow plug in the engine must fall within a strictly defined range for the application of a pulse-width modulated signal to each glow plug to be effective. In Chevrolet speak, the differences between the electrical resistances of the glow plugs are known as “offsets” from an ideal value and when the offset from an ideal value on any given glow plug exceeds a maximum allowable limit, the glow plug control module cannot control the heating of that glow plug effectively.

Thus, in the case of code P133E, the glow plug control module has detected that the offset value on glow plug #7 has exceeded a maximum allowable limit when the glow plug is hot, and it will set code P133E as a result. In some cases, the glow plug control module will also illuminate a warning light upon the first failure of the glow plug.

Where is the P133E sensor located?

This image shows the locations (red arrows) of some glow plugs on some 6.5L Chevrolet V8 diesel engines. The orange wires are the power feeds to the glow plugs.

In this case, the glow plugs are protected by steel heat shields that must be removed from the engine by loosening the nuts indicated by the yellow circles, but be aware that removing these nuts without breaking the studs they screw onto can be challenging even for professional mechanics.

As a general rule, though, we recommend that you seek professional assistance with removing or replacing glow plugs on any Chevrolet engine because there is a high likelihood that inexperienced non-professional mechanics might break glow plugs during the removal process. If this happens, it might be necessary to remove the cylinder head from the engine to remove the glow plug remnant from the cylinder head.

What are the common causes of code P133E?

Some common causes of code P133E could include one or more of the following-

  • Defective or malfunctioning glow plug in cylinder #7
  • The use of a substandard aftermarket glow plug on cylinder #7
  • Poor or damaged electrical connection on glow plug #7
  • Damaged or burnt wiring on glow plug #7
  • Damaged or corrupted glow plug driver circuit on cylinder #7
  • Failure to perform a glow plug relearn procedure after a glow plug replacement
  • Failed or failing glow plug control module

NOTE: Chevrolet TSB 20-NA-176 dated September 2020 addresses code P133E on several Silverado and GMC Sierra models. In these cases, the code is attributed to software failures that can be corrected by reprogramming the glow plug control module with updated software using dealer-grade equipment and following OEM procedures. TSB 20-NA-176 is available here, so be sure to consult it to see if your vehicle is affected.

What are the symptoms of code P133E?

The only symptom of code P133E is likely to be a stored trouble code and an illuminated warning light, but note that according to the TSB referenced above, the presence of some, or all of the following codes could contribute to the setting of code P133E on some Chevrolet and GMC vehicles-

P1338, P1339, P133A, P133B, P133C, P133D, , P133F, P066A, P066B, P066C, P066D, P066E, P066F, P0671, P0672, P0673, P0674, P0675, P0676, P0677, P0678, P067A, P067B, P067C, P067D, P067E and/or P067F

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