P0651 code

Tiny
COREAVE
  • MEMBER
  • 2008 CHEVROLET COBALT
  • 2.2L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 170,000 MILES
5vB is missing (5v2).
Friday, September 13th, 2019 AT 6:52 PM

3 Replies

Tiny
JIS001
  • MECHANIC
  • 3,411 POSTS
Hello and welcome to 2CarPros. Here is a circuit description so you can see what is controlled on the 5 volt reference:

Collision

 62

2008 Chevrolet Cobalt

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L4-2.2L

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P0651

Vehicle ALL Diagnostic Trouble Codes ( DTC ) Testing and Inspection P Code Charts P0651

P0651

DTC P0641 or P0651

Diagnostic Instructions

 *  Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Vehicle > Initial Inspection and Diagnostic Overview
 *  Review Strategy Based Diagnosis for an overview of the diagnostic approach.
 *  Diagnostic Procedure Instructions provides an overview of each of the diagnostic category.

DTC Descriptors

DTC P0641
 -  5-Volt Reference 1 Circuit

DTC P0651
 -  5-Volt Reference 2 Circuit

Diagnostic Fault Information

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Circuit/System Description

The engine control module (ECM) has 2 internal 5-volt reference busses called 5-volt reference 1 and 5-volt reference 2. Each reference buss provides 5-volt reference circuits for more than one sensor. A fault condition on one 5-volt reference circuit will affect the other 5-volt reference circuits connected to that reference buss. The ECM monitors the voltage on the 5-volt reference buss.

The 5-volt reference 1 buss provides 5 volts to the following sensors:

 *  The manifold absolute pressure (MAP) sensor
 *  The fuel tank pressure (FTP) sensor
 *  The air conditioning (A/C) refrigerant pressure sensor
 *  The accelerator pedal position (APP) sensor 2
 *  The exhaust camshaft position (CMP) sensor
 *  The intake CMP sensor

The 5-volt reference 2 buss provides 5 volts to the following sensors:

 *  The APP sensor 1
 *  The throttle position (TP) sensor 1 and 2
 *  The crankshaft position (CKP) sensor
 *  The secondary air injection (AIR) solenoid

At the throttle body, back probe the grey wire on the connector with key on engine off. Since the 5 volts is missing, unplug the connector with the probe still attached. If the 5 volts comes back on the throttle is bad. If no 5 volts then start unplugging every component on bus 2. The APP is the accelerator pedal so unplug it. If the 5 volts comes back on then the APP is bad and if not unplug every component until you get 5 volts back. Let us know what the test results are.

You can also work backwards and unplug everything in that circuit and plug one item at a time until you lose the 5 volts to isolate the problem. If you have any questions, don't hesitate to ask.
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Friday, September 13th, 2019 AT 9:36 PM
Tiny
COREAVE
  • MEMBER
  • 2 POSTS
Turned out to be Secondary Air Injection Shut-Off and Check Valve found one at junk yard $25 all fixed. Thanks for your guidance
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Tuesday, September 17th, 2019 AT 9:30 PM
Tiny
JIS001
  • MECHANIC
  • 3,411 POSTS
Hello and welcome back. Glad to hear you were able to narrow it down to the air injection. Please use 2CarPros if you ever need our assistance again.
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Tuesday, September 17th, 2019 AT 9:37 PM

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