ScanMaster & Engine Sensor Codes
- I generally spend a lot of time researching problems because I like to have an understanding of what's going on. Like most people, I hate not knowing something. Since I'm having to do research and gather information, I'll share it with anyone who might be interested or going down the same road as I am. I am by no means an expert - I'm just someone who has a need to know. And I like working on my own vehicle! If you find something in error or have some knowledge you can add, please E-Mail me and let me know! Additional information has been provided by Fred Forsythe (Fred Injun-eer). Thanks Fred!
ScanMaster Code Index:
MPH, MAF, SP, LP, RP, MAL, DTC, LBL, RBL, CEL, LIN, RIN, LO2, RO2, ATS, IAT, CLT, TPS, TPP, IAC, EGR, MAP, BAR, ACP, CCP, Knock
Vehicle sensor codes and descriptions:
This is the vehicle's speed in Miles Per Hour. The ECM determines the vehicle's speed by monitoring the Vehicle Speed Sensor (VSS). On our 4th Gen F-bodys, the VSS is located on the back of the transmission, and generates the electrical pulses. This sensor delivers a stream of pulses to the ECM whose frequency is proportional to vehicle speed. The ECM monitors this pulse stream and uses the data for various functions including Torque Converter Clutch (Lockup) and Cruise Control operation. A malfunction of the Vehicle Speed Sensor should cause trouble code 24 to be set. A fault in this circuit should be indicated only while the vehicle is in motion. Disregard code 24 if set when drive wheels are not turning (According to the Haynes Manual). Check connection at the ECM/PCM. Check the TPS setting as well.
The engine coolant temperature is displayed in degrees of Fahrenheit on the ScanMaster. The coolant temperature signal is provided to the ECM by the coolant temperature sensor (CTS). This sensor is located in the front of the engine on the water pump. The device is a thermistor, and the resistance varies inversely with the temperature. Information obtained from this sensor allows the ECM to control the vehicle's spark advance, air/fuel ratio, idle speed, temperature light operation, and various switching functions such as exhaust gas recirculation (EGR) and torque converter lockup. A malfunction of this sensor should cause trouble code 14 or 15 to be set. Codes 14 & 15(Coolant Sensor Circut) If the engine is experiencing overheating problems, the problem must be rectified before continuing. Check all wiring and connectors associated with the sesor. Replace the cooland sensor if necesary. Also check the thermostat for proper operation and that coolant levels are correct.
ATS (IAT) - Intake Air Temperature Sensor
This is the intake Manifold Air Temperature. The IAT sensor is a thermister device whose electrical resistance varies inversely with temperature, and is mounted on the engine's intake tube elbow, immediately before the throttle body. A malfunction of the IAT sensor should set trouble code 23 or 25. For problems, check the IAT sensor. Check for wiring and connection to the sensor. Replace the IAT sensor if necessary.
MAP - Manifold Absolute Pressure
This is the intake manifold pressure measured in Inches of Mercury. Manifold pressure is monitored by the Manifold Absolute Pressure (MAP) sensor. This sensor is the flexible resistor type whose electrical resistance varies with pressure changes. Manifold pressure is the opposite of manifold vacuum, hence the MAP sensor provides information similar to a vacuum sensor which it is used in place of. The MAP sensor allows the ECM to monitor engine load. A malfunction of this sensor should set trouble code 33 or 34. The MAP sensor is located on top the Intake Manifold towards the front, passenger side, just after the throttle body. The numerical difference between MAP (e.g. - 9.5 @ idle) and BAR
(e.g. 30 at sea level) = 20.5 = vacuum.
The barometric pressure sensor is used to sense ambient atmospheric pressure changes due to altitude or weather fluctuations. Pressure readings are displayed in Inches of Mercury. This sensor is a flexible resistor type and provides a variable voltage to the ECM that depends upon the current barometric pressure. The sensor's output voltage is usually between 2.5 and 5 volts. The ECM uses the barometric sensor in conjunction with the manifold pressure sensor to determine manifold pressure for a given altitude. These pressure readings allow the ECM to make spark timing and air/fuel ratio modifications. The average atmospheric pressure at sea level is approximately 30 inches of mercury (Hg).
TPP - Throttle Position Percent
This displays the current throttle position in percent from 0 to 100. The ECM monitors the throttle's position by reading the Throttle Position Sensor. This sensor is the variable resistance type and is mechanically connected to the throttle mechanism. The voltage returned to the ECM by the Throttle Position Sensor increases as the throttle opening increases and is in the range of approximately 0 to 5 volts. A malfunction of this sensor should cause trouble code 21 or 22 to be set.
TPS - Throttle Position Sensor Volts
This is the voltage returned to the ECM by the Throttle Position Sensor. This sensor is used by the ECM to monitor the throttle plate angle and returns a voltage in the range of 0 to 5 volts. A malfunction of the Throttle Position Sensor should cause trouble code 21 or 22 to be set. For problems, check for a sticking TPS. Check all wiring and connection sat the TPS and at the ECM/PCM. Replace if necessary. This device is not adjustable on the stock throttle body, however some aftermarket throttle bodies may allow you to adjust this. Range is 0.50-0.67 closed, and ~4.5V at WOT.
LO2/RO2 - Left & Right Bank Oxygen Sensors
Trouble codes for O2 sensors are 63, 64, and 65 for the right bank, and 13, 44, and 45 for the left bank. Although my Haynes manual shows a code 55 for "Fuel Lean Monitor" on the 5.7L engines which indicates engine running lean during power acceleration, indicating a possible fuel pump failure, fuel pressure regulator failure, or restricted fuel line.
Good values to look for here under WOT are between 850 and 900. Some people have experienced better power towards the lower side without detonation. With an AFPR (Adjustable Fuel Pressure Regulator) you can adjust your pressure up or down. Be aware that you are only looking for WOT values with the AFPR as the ECM will correct for most adjustments you make for part-throttle operation, and for somewhat for WOT operation.
LP/RP - Left & Right Injector Pulse Width
This is the fuel injector ON time in milliseconds. Injector ON time is calculated and controlled by the ECM and is dependent upon engine speed and load. The amount of fuel being delivered to each cylinder is directly proportional to this value.
This data field displays Idle Air Position counts. On fuel injected vehicles, engine idle speed is controlled by the Idle Air Control motor. Commanded by the ECM, the IAC maintains idle speed by varying the size of an air channel that bypasses the engine's throttle plate. By allowing additional air into the intake manifold, the IAC compensates for engine temperature and load variations. The IAC motor retracts and extends in small increments commonly referred to as counts. A count of 255 indicates maximum bypass and full IAC retraction, whereas a count of 0 indicates no bypass and full IAC extension.
CCP - Carbon Canister Pressure
The charcoal carbon canister is part of the vehicle's Evaporative Emission Control System and is purged by a vacuum operated purge valve. The ECM controls vacuum to this valve through the Canister Purge Solenoid. This data field displays the percentage of time the canister is being purged over a predetermined time interval. On most vehicles the purge solenoid is energized to inhibit purging and de-energized to permit purging of the charcoal canister. This solenoid is energized during a cold engine condition and is de-energized after warm-up when the engine is above a specified RPM. Canister purge allows collected fuel vapors in the canister to be drawn into the intake manifold for burning. Canister purge on some vehicles is controlled through a combined EFE/EGR/Canister Purge solenoid unit.
This is the total spark advance applied to the engine's ignition system by the ECM. Spark advance values are displayed in Degrees. Your total timing being used by the engine is this value, which has taken in account for the retard amount applied by the Knock Sensor (KS) circut. (As controlled by the Knock Module (KM) in the ECM).
Knock Retard - On the ScanMaster's default display mode
Knock Retard values relate to the amount of spark retard the Electronic Spark Control (ESC) unit is applying to the ignition system. Knock Retard will be displayed in degrees (DEG). The ESC monitors the engine Knock or Detonation sensor for vibrations caused by detonation. Upon sensing a detonation, the ESC sends a command to the distributor to retard the timing at a rate of approximately 4 degrees per second until the detonation stops. After this adjustment has been made, the ESC advances the timing at a slower rate than it was originally retarded at. A slight amount of engine Knock is normal with this type of control. One method used to combat false knock, if you are experiencing it, is to replace your LT1 knock module with an LT4 knock module. The LT4 Knock Module makes a more accurate measurement of true knock by filtering out extraneous engine noises that produce false knock. See LT4KM Mod in the Projects area for more information on how to do this.
LIN/RIN (LBL/RBL) - Left & Right Integrator
This is the ECM's Integrator value. This is short-term fuel correction - works like block learn. When an engine is running in its Closed Loop mode, Integrator values relate to short term adjustments that are made to the quantity of fuel an injector is delivering. The ECM controls fuel delivery by varying the length of time that an injector remains on. Integrator values are calculated by the ECM and depend upon readings from the oxygen sensors. The Integrator has a nominal value of 128 and is raised or lowered from this point in order to maintain an ideal 14.7 to 1 air/fuel ratio. When the ECM detects a rich exhaust mixture, it decreases the Integrator value and thereby decreases injector ON time. When a lean exhaust mixture is detected, the ECM increases the Integrator value and thereby increases injector ON time. The Integrator can adjust fuel delivery over a wide range for short time periods. If a long term fuel adjustment needs to be made, the Integrator causes a change in the ECM's Block Learn value. Block Learn values affect fuel delivery in the same fashion as Integrator values, but have a smaller impact and remain in effect for a longer period of time. The Integrator and Block Learn values have a range of 0 to 255.
The operating range of the vehicle's engine for any combination of RPM and load is divided into several Blocks (about 18 Cells), therefore during normal vehicle operation, the engine is always operating in one of these Blocks. The ECM has a predetermined fuel delivery value for each Block stored in its internal memory. As the engine's operating characteristics cause it to enter a particular Block, the ECM uses its stored fuel delivery value to set the air/fuel mixture. Should the ECM sense that this value is not providing an ideal 14.7 to 1 air/fuel ratio, it adjusts the Block Learn value to correct the condition. Consistently high or low Block Learn values may indicate fuel delivery, fuel pressure, EGR, or other fuel system problems. For instance, plugged fuel injectors would cause the Block Learn value to increase, thereby increasing injector on time to compensate for the restricted fuel passage.
CEL - Fuel Cell, Long-term fuel correction
The Block Learn Cell Number displays which of the engine load cells the ECM is currently using for fuel calculations. Block Learn Cells are simply locations created by the ECM in its internal memory and are used to store Block Learn Multiplier values. Block Learn values correspond to fuel injector ON time. The operating range of the vehicle's engine for any combination of RPM and load is divided into several Blocks (regions), therefore during normal vehicle operation, the engine is always operating in one of these Blocks. The ECM has a predetermined fuel delivery value for each Block stored in its internal memory. As the engine's operating characteristics cause it to enter a particular Block, the ECM uses its stored fuel delivery value to set the air/fuel mixture. Should the ECM sense that this value is not providing an ideal 14.7 to 1 air/fuel ratio, it adjusts the Block Learn value to correct the condition. There are about 16 closed loop cells and two open loop cells (17 and 18?). The cells are a grid with RPM on one axis and MAP on the other.
This is the amount of air entering the engine as measured by the MAF. Air flow rate is displayed in grams per second (GPS). This information is delivered to the ECM by the Mass Air Flow sensor and is used to control fuel delivery to the engine. A malfunction of this sensor should cause trouble code 48 to be set.
Notes from Fred: I think that the max reading on the stock MAF is 255. This is an 8-bit binary signal, so, like several of the other measurements, there can only be 256 steps (0-255). That's why the increment of RPM is 25 rpm on the scanner. I think the max may be 255 x 25 = 6375rpm, but I have never tested this theory. If rpm can go above 6375, and still be read, this idea goes out the window. Same with MAF, I guess. On ws6.com, with the TTS sample display, he is cranking 5700 rpm/WOT and his MAF reading is 235.
Note: I need more information on this! Anyone know what the MAX value for stock programming is on this, and what it can be extended to for supercharged applications from custom coding like Hypertech, etc. Anyone have specifics for me on this?
EGR - Exhaust Gas Recirculation Valve duty cycle
Exhaust Gas Recirculation is controlled by the ECM through a solenoid operated vacuum valve. Upon receiving data from various engine sensors, the ECM operates the EGR solenoid, which is usually located in the EGR valve's vacuum control line. When normal engine operating temperatures are present, the EGR solenoid is de-energized. This condition allows engine vacuum pressure to operate the EGR valve, thus allowing exhaust recirculation. When the recirculation of exhaust gases is not desirable, the EGR solenoid is energized, blocking engine vacuum pressure to the valve. This condition usually occurs during periods of wide open throttle, engine cranking, low coolant temperature, or engine idling. This data field displays the duty cycle of the EGR solenoid in percent. Duty cycle refers to solenoid ON time versus OFF time. A reading of 30% would indicate that the solenoid is ON for 30% of the maximum time possible. Exhaust Gas Recirculation is used to reduce oxides of nitrogen which form during the combustion process. Reduction of these oxides is accomplished by lowering engine combustion temperatures. EGR allows small amounts of exhaust gas to be recirculated back into the intake manifold which thereby reduces combustion temperatures by as much as 500 F, thereby reducing detonation. Problems with this can set code 32.
ACP - Air Conditioner Pressure
This is the Air Conditioning system's pressure sensor voltage. This pressure sensor is normally located on the high pressure side of the freon circuit and has a range of 0 to 5 volts. Monitored by the ECM, this sensor allows the ECM to compensate for the additional engine load created by the A/C compressor.
MAL/DTC - Malfunction Code / Diagnostic Trouble Code
This is the code returned from the ECM to indicate an error condition. This is picked up by the ScanMaster and may be a real time or stored code. Some of the functions (i.e. 18 - Injector Circut problem) do not turn on the Service Engine Soon (SES) light.
That's it so far - more to come as research continues. If you have any information you'd like to add, pleases feel free to E-mail me any information you think would be valuable.
