Question about 2002 Chevrolet Blazer

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2002 s10 blazer code p1638 generator f terminal fault what is this code indicate is wrong if the starting and charging system is good?

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My truck had this. if you ever notice your lights flickering very slightly somtimes at night? (dash lights or dome light) it means your alternetor may be goin out.

Posted on Apr 07, 2011

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The PCM (powertrain control module) uses the generator field duty cycle signal circuit to monitor the duty cycle of the generator. The GM PCM is set to expect a charging system field of 0 to 30% when the key is off and the engine is not running. If it sees more or does not see any a code is stored. When the engine is running the PCM is set to see a charging field duty cycle of 0 to 100%.A PennTex GM replacement charging system (prior to 2008) normally has 11 to 12 volts on the blue field wire. (100% field duty cycle) with the key on and the engine off. This being more than the 30% the PCM expects to see causes a code to be stored. If the charging system has been verified then the code can be treated as informational. This was a known issue published by PennTex USA on 10/1/2008.

I hope this helped. God Bless.

Posted on Apr 07, 2011

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Posted on Jan 02, 2017

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P2500 starts but won't stay running


P2500 Generator Lamp/L-Terminal Circ Low

Indicator

This code indicates that a fault has been detected in the generator lamp control circuit. The PCM may have also detected an abnormal voltage reading from the vehicle battery, starting, or charging system.

Code Set Parameters

In the event of generator lamp control circuit fault, a trouble code will be stored and a service engine soon lamp will be illuminated. Some models require multiple drive cycles (as many as 8) with a failure in order for the service engine soon lamp to be illuminated and others will activate it on the initial failure.

Symptoms

This code indicates that a fault has been detected in the charging system circuit. The PCM may have also detected an abnormal voltage reading from the vehicle battery, starting, or charging system.

Common Causes

The most common cause of this code can be traced to a faulty alternator. Other causes could include a bad battery or starter, open or shorted wiring or battery cables, insufficient battery primary or secondary grounds, defective voltage regulator, corroded battery terminal ends, a faulty PCM (rare), a large battery drain, or a defective battery.

Common Misdiagnosis

Technicians report that batteries and starters are often replaced in error when the alternator is either not charging or overcharging. If the battery is discharged, charge it and test the vehicle charging system to make sure that it is operating properly.

Diagnosis

  • The starting/charging system is monitored by the PCM whenever the key is placed in the "ON" position, as is the generator lamp circuit for the instrument panel
  • When the engine is running, the PCM is programmed to anticipate between 13.8 and 14.4 volts from the charging system
  • If a voltage reading that either exceeds or underachieves, a code will be stored and a service engine soon lamp illuminated
  • Some vehicle models (especially Chrysler) also use the PCM to regulate charging system voltage
  • System voltage malfunctions related to the PCM are much more common in vehicles equipped with this type of system than in other systems. Before beginning your diagnosis, make sure that the battery is fully charged
  • If the battery fails to take or hold a charge, it should be replaced. Several tools will be instrumental in successfully diagnosing this code
  • A suitable OBD-II scanner (or code reader) and a digital volt/ohmmeter will be most helpful in performing a successful diagnosis
  • Begin with a visual inspection of all wiring and connectors
  • Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
  • Always retest the system after repairs are completed to ensure success. If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
  • This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
  • Continue by clearing the code and operating the vehicle to see if it returns
  • This will help to determine whether or not the malfunction is intermittent
  • After the codes are cleared, test drive the vehicle to see if the code returns
  • If the code fails to immediately return, you may have an intermittent condition
  • Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made
  • Continue with a visual inspection of the battery and battery cables
  • Should you find excessive corrosion on the battery terminals, suspect a poor battery connection
  • If this is the case, disconnect the battery cables from the battery (always disconnect the ground cable first and see manufacturer's recommendations for disconnecting/reconnecting the battery) and remove the corrosion from the battery posts and terminals
  • Reconnect the battery and retest the charging system
  • Connect the starting/charging system tester to the battery and perform a load test
  • If the battery fails the load test, replace it
  • If the battery passes the load test, leave the tester connected and start the engine
  • Observe the voltage readings on the tester and compare your findings with manufacturer's specifications
  • Replace starting/charging system components as required
  • Typical alternator output should read approximately 14 volts with the engine started and no accessories or lighting turned on
  • Leave the tester connected and use the amp probe to test the starter current draw
  • Compare your findings to manufacturer's specs and repair or replace starting system cables or other components as needed. The generator lamp circuit is used to activate a charging system indicator in the instrument panel if system voltage is abnormal
  • Voltage readings that are too low may indicate worn brushes in the alternator
  • High voltage readings may be indicative of a defective voltage regulator (usually integrated in the alternator but some are part of the PCM)
  • Before performing any continuity and resistance testing on the generator lamp circuit, be sure to disconnect the wiring from the instrument panel to prevent damage to system controllers and circuit boards
  • Consult the vehicle service manual for reference voltage readings and other precautions. If the starting/charging system are in proper working order, you will need to test secondary wiring
  • Disconnect the alternator connector and test all circuits using the digital volt/ohmmeter
  • If alternator wiring values are in line with acceptable specifications, disconnect the PCM connector and perform a continuity test on all system circuits
  • Compare actual findings with manufacturer's specifications and repair open or shorted electrical wiring as necessary. If the malfunction has still not been rectified, suspect a defective PCM.

Nov 09, 2016 | Cars & Trucks

1 Answer

I have a 2002 chevy tahoe 4X4 with a 5.3L that has set a P1258 code engine over temp, it has also set a P0117 ect low input code, and a P1637 L terminal circuit, P1638 F terminal circuit codes.


If these codes are being only set during start I would expect a failure of the battery. If the voltage goes much below 9 VDC the computers (EMS) can become erratic and codes and limp home modes are a common result of defective and discharged batteries!



Careful having the battery tested. Any arcing etc at the battery can be the kiss of death for the engine computer. Better to remove terminal to check. Or test the crank voltage with multi-meter.

Mar 05, 2016 | Cars & Trucks

1 Answer

99 Chevy S10 Blazer that seems to start in second gear


run fault codes to check for servo/ solenoid problems --TCM faults

Jan 28, 2014 | Cars & Trucks

1 Answer

Code p1638 2003 blazer


Alternator F terminal circuit. Check your plug-in in the Alternator case. The field wire is not connecting. You could have a bad supply wire from the Ignition switch or a Relay.

Check with Autozone.com and register your vehicle for free wiring diagrams and fusebox layouts. Some GM vehicles use Relays or fuses in the charging circuit.

Nov 03, 2012 | 2003 Chevrolet Blazer

1 Answer

P1638


My 03 yukon xl has been showing a message on the cluster saying battery not charging and the battery light and message blinks on and off.but got everything tested and everything is good battery alternator fuses wires everything.but when ac is on i lose power and can't drive all day and it will start boring out.so we checked it on the scan and a p1638 code is poping up and saying to check f terminal but can't find it.need help

Jun 04, 2012 | 2000 GMC Yukon XL

1 Answer

2003 s-10 changed motor, now won't start. you can


CODE P1637 - GENERATOR L TERMINAL CIRCUIT MALFUNCTION CONDITIONS. CODE P1638 - GENERATOR F TERMINAL CIRCUIT MALFUNCTION CONDITIONS. POSSIBLE CAUSES FAULTY GENERATOR WHICH IS ALTERNATOR.CHECK GENERATOR POWER FEED WIRES AND CHECK GENERATOR VOLTAGE REGULATOR WIRES FOR LOOSENESS AND DAMAGE. MAKE SURE BATTERY VOLTS ARE 12.6 VOLTS. IF BATTERY WEAK DUE BAD GENERATOR VECHICLE WONT START.

Sep 23, 2011 | 2003 Chevrolet S-10

1 Answer

My s type jaguar dtc p1638 i dont undarstand the mining of that why, 2000 year it asking me to look in the manual tecnical book


Fault codes are listed in the technical handbook, no good to you as it's a Jaguar service item unless you can get a copy of JTIS from ebay etc.


Fault Code:- P1638 Indicates a Power-train fault


The fault is generally due to a problem in the Computer & Output Circuit area


Fault Description: CAN ECM / INST network malfunction

Action of ECM:- none


After clearing the DTC, complete the Ignition ON 10 seconds
Check for a reoccurrence of fault DTC.


Possible Fault:- CAN open circuit fault - INST to ECM CAN short circuit fault INST failure ECM failure D

May 26, 2011 | 2003 Jaguar X-Type

1 Answer

2000 chevy s10 blazer cranks but won't start????


Check for gas or spark problem on the engine. Check that starting fluid does start the car for a few seconds before dying, indicating a fuel delivery problem, like a fuel pump or circuit to it.

If the car won't start with starting fluid sprayed into the intake, then the ignition system may be at fault, or engine timing.

Dec 12, 2010 | 2000 Chevrolet Blazer

1 Answer

Where do i put the papper clip in a 1992 s10 blazer to get the check engein light to blink the code


1992.... right ????it wont work on a 2002. farthest right upper and lower terminals.

Oct 11, 2009 | 2002 Chevrolet S-10

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