Ford Mustang (1999-2004) Service Manual: Pinpoint Test O: DTC B1870 - Air Bag Indicator Shorted to Battery

Normal Operation

The air bag indicator is designed to illuminate for 6 (+/-2) seconds when the ignition switch is turned to the RUN position. This initial 6 seconds of illumination is considered normal operation and is called proveout of the air bag indicator. The air bag indicator is then used to warn the driver that there is a fault in the air bag supplemental restraint system (SRS).

While the air bag indicator is lit, the restraints control module (RCM) monitors the air bag indicator for short to battery conditions. If the RCM detects a short to battery condition on the air bag indicator circuit, it will store a diagnostic trouble code (DTC) B1870 in memory.

If the RCM detects an air bag indicator failure in addition to another SRS failure, the RCM will send a signal to the generic electronic module (GEM) to produce five sets of five tone bursts.

Possible Causes

An air bag indicator short to battery condition can be caused by:

  • damaged wiring on circuit 608 (BK/YE).
  • an instrument cluster malfunction.
  • an RCM internal concern.

PINPOINT TEST O: DTC B1870 - AIR BAG INDICATOR SHORTED TO BATTERY

Test Step Result / Action to Take
O1 CHECK FOR A HARD OR INTERMITTENT DTC Yes

This is a hard fault. The fault condition is still present. This fault cannot be cleared until it is corrected and the DTC is no longer retrieved during the ondemand self test.

GO to O2 .

No

This is an intermittent fault.

The fault condition is not present at this time. GO to O4 .
  • Key in OFF position.
  • Connect the diagnostic tool. Scan Tool
  • Key in ON position.
  • Enter the following diagnostic mode on the diagnostic tool: Retrieve/Clear Continuous DTCs.
  • Retrieve and record any continuous DTCs for use later in this pinpoint test.
  • Enter the following diagnostic mode on the diagnostic tool: On- Demand Self Test.
  • Was DTC B1870 retrieved during the on-demand self test?
O2 CHECK THE AIR BAG INDICATOR CIRCUIT Yes

INSTALL a new RCM. GO to O5 .

No

GO to O3 .
WARNING: If the supplemental restraint system (SRS) is being serviced, the system must be deactivated and restraint system diagnostic tools must be installed. Refer to Air Bag Supplemental Restraint System (SRS) in this section.

The air bag restraint system diagnostic tools must be removed and the air bag modules reconnected when the system is reactivated to avoid non-deployment in a collision, resulting in possible personal injury.

NOTE: Diagnostics or repairs are not to be performed on a seat equipped with a seat side air bag with the seat in the vehicle. Prior to attempting to diagnose or repair a seat concern when equipped with a seat side air bag, the seat must be removed from the vehicle and the restraint system diagnostic tools must be installed in the seat side air bag electrical connectors. The restraint system diagnostic tools must be removed prior to operating the vehicle over the road.

NOTE: After diagnosing or repairing an SRS, the restraint system diagnostic tools must be removed before operating the vehicle over the road.

NOTE: After diagnosing or repairing a seat system, the restraint system diagnostic tools must be removed before operating the vehicle over the road.

NOTE: The SRS must be fully operational and free of faults before releasing the vehicle to the customer.

  • Key in OFF position.
  • Deactivate the system. Refer to Air Bag Supplemental Restraint System (SRS) in the Diagnosis and Testing portion of this section.
  • Key in OFF position.
  • Disconnect: RCM C2041.
  • Key in ON position.
  • Is the air bag indicator illuminated?
O3 CHECK AIR BAG INDICATOR CIRCUIT FOR SHORT TO BATTERY Yes

REPAIR the instrument cluster.

GO to O5 .

No

REPAIR the circuit. GO to O5 .
  • Key in OFF position.
  • Disconnect: RCM C2041.
  • Disconnect: Instrument Cluster C220a.
  • Key in ON position.
  • Measure the voltage between RCM C2041 pin 20, circuit 608 (BK/YE), harness side and ground.

  • Is the voltage less than 0.2 volt?
O4 CHECK FOR AN INTERMITTENT FAULT Yes

CHECK for causes of intermittent short to battery on circuit 608 (BK/YE). Attempt to recreate the hard fault by flexing the wire harness and cycling the ignition key frequently.

REPAIR any intermittent concerns found.

GO to O5 .

No

GO to O5 .
  • Refer to the continuous DTCs recorded during Step O1.
  • Was the continuous DTC retrieved during Step O1 an intermittent fault?
O5 CHECK FOR ADDITIONAL DTCs Yes

Do not clear any DTCs until all DTCs have been resolved. GO to the Restraints Control Module (RCM) Diagnostic Trouble Code (DTC) Priority Table in this section for pinpoint test direction.

No

RECONNECT the system.

REACTIVATE the system. PROVE OUT the system.

REFER to Air Bag Supplemental Restraint System (SRS) in this section. CLEAR all DTCs.
  • Refer to the continuous DTCs recorded during Step O1.
  • Were any continuous DTCs retrieved during Step O1?
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